ABSTRACT
While comprehensive mental health promotion inherently involves individuals, there is an ongoing need to address large-scale determinants of people's mental health and wellbeing-particularly policies and environments. To have the best possible chance of creating positive change, mental health promotion must also work throughout key mediating structures such as places of education and work. This includes universities. Yet, in their efforts to address student and staff mental health and wellbeing, Australian universities have demonstrated limited uptake of comprehensive mental health promotion approaches. In this commentary, I discuss a recent review of Australia's higher education system-the Australian Universities Accord-as a catalyst for strengthening institutional action and change through a comprehensive mental health promotion lens. I discuss key findings-and silences-made clear throughout the review process. I then advocate several urgent priorities for university-level change-across institutional assessment, institutional accountability and performance, and institutional leadership and power-if Australia's universities are genuinely committed to improving mental health and wellbeing among students and staff.
ABSTRACT
Sexual violence is prevalent on university campuses globally. In this article, we report a qualitative insider research study examining practices for addressing sexual violence at four universities across Australia and Aotearoa New Zealand. We collected, analysed, and synthesised descriptive information about the practices at each institution. We found unique institutional approaches that nonetheless share some commonalities, yieldingseveral themes that are central to practice. In reflecting on our findings, we conclude with an outline of critical considerations and a call to action for future efforts to address campus-based sexual violence, particularly as this field remains underdeveloped across Australia and Aotearoa New Zealand.
Subject(s)
Sex Offenses , Humans , New Zealand , Qualitative Research , Universities , AustraliaABSTRACT
Objectives: This study aimed to evaluate the socioeconomic inequality in gastric cancer (GC) screening in Korea. Socioeconomic inequality was assessed using both organized and opportunistic screening according to income and educational level. Methods: GC screening data were obtained from the 2009-2022 Korean National Cancer Screening Survey. The final analysis included 47,163 cancer-free men and women. The weighted cancer screening rate was estimated using joinpoint regression. The inequality indices were measured in terms of both the absolute slope index of inequality (SII) and the relative index of inequality (RII) using the Poisson regression model. Results: The organized screening rate for GC increased from 38.2% in 2009 to 70.8% in 2022, whereas the opportunistic screening rate decreased from 18.8 to 4.5%. Regarding educational inequality, a negative SII value was observed [-3.5, 95% confidence interval (CI), -7.63-0.83%] in organized screening, while a positive SII (9.30%; 95% CI, 6.69-11.91%) and RII (1.98%; 95% CI, 1.59-2.46) were observed in opportunistic screening. Furthermore, income inequality was not found in organized GC screening; however, overall SII and RII for opportunistic screening were 7.72% (95% CI, 5.39-10.5) and 1.61 (95% CI, 1.42-1.81), respectively. Conclusion: Organized screening rates have grown gradually over time and account for the majority of GC screenings in South Korea. While no socioeconomic inequalities were found in organized screening, significant socioeconomic inequalities were found in opportunistic screening.
Subject(s)
Early Detection of Cancer , Stomach Neoplasms , Male , Humans , Female , Socioeconomic Factors , Stomach Neoplasms/diagnosis , Stomach Neoplasms/epidemiology , Health Status Disparities , Republic of Korea/epidemiologyABSTRACT
OBJECTIVES: This study aimed to investigate socioeconomic status (SES)-based inequality in colorectal cancer (CRC) screening in Korea. We assessed whether the rates of opportunistic and organized CRC screening differed according to income and education levels. METHODS: We analyzed data from the Korean National Cancer Screening Survey of 27,654 cancer-free individuals, aged 50-74 years, from 2009 to 2021. The weighted cancer screening rates with trends were estimated with the average annual percentage change using joinpoint regression. Inequality was calculated in both relative and absolute terms, based on a Poisson regression model. RESULTS: The organized screening rate increased significantly from 22.1% in 2009 to 53.1% in 2020 and 50.6% in 2021, with an average annual change of 8.6% (95% confidence interval [CI], 4.9 to 12.5). In contrast, no significant trend was observed for opportunistic screening. The SES inequality in opportunistic screening uptake was indicated by a slope index of inequality (SII) of 9.74% (95% CI, 6.36 to 13.12), relative index of inequality (RII) of 2.18 (95% CI, 1.75 to 2.70) in terms of education level; and an SII of 7.03% (95% CI, 4.09 to 9.98), RII of 1.81 (95% CI, 1.41 to 2.31) in terms of measured income. Although there was an increasing trend in income inequality, no significant SES inequalities were observed in the overall estimates for organized screening. CONCLUSIONS: Organized CRC screening is effective in improving the participation rate, regardless of SES. However, significant inequalities were found in opportunistic screening, suggesting room for improvement in the overall equity of CRC screening.
Subject(s)
Colorectal Neoplasms , Early Detection of Cancer , Humans , Socioeconomic Factors , Healthcare Disparities , Colorectal Neoplasms/diagnosis , Colorectal Neoplasms/epidemiology , Republic of Korea/epidemiology , Health Status DisparitiesABSTRACT
Trichoderma reesei is the most well-known cellulase producer in the biorefinery industry. Its cellulase biosynthesis is repressed by glucose via carbon catabolite repression (CCR), making CCR-releasing strains with cellulase hyperproduction desirable. Here, we employed a microfluidic droplet platform to culture and screen T. reesei mutants capable of CCR release and cellulase overproduction from extensive mutagenesis libraries. With 3 mutagenesis rounds, about 6.20 × 103 droplets were sorted from a population of 1.51 × 106 droplets in a period of 4.4 h; 76 recovery mutants were screened on flask fermentation, and 2 glucose uptake retarded mutants, MG-9-3 and MG-9-3-30, were eventually isolated. We also generated a hypercellulase producer, M-5, with CCR release via a single mutagenesis round. The hyphal morphology and molecular mechanisms in the mutants were analyzed. This versatile approach combined with a comprehensive understanding of CCR release mechanisms will provide innovative and effective strategies for low-cost cellulase production.
Subject(s)
Catabolite Repression , Cellulase , Trichoderma , Trichoderma/genetics , Cellulase/genetics , Cellulase/metabolism , MicrofluidicsABSTRACT
BACKGROUND: The Korea National Cancer Screening Program (KNCSP) offers upper endoscopy or upper gastrointestinal series (UGIS) biannually for people aged ≥ 40 years. This study aimed to assess the effect of negative screening results on the incidence of and mortality from upper gastrointestinal (GI) cancer. METHODS: A population-based retrospective cohort of 15,850,288 men and women was constructed using data from 3 national databases. The participants were followed until the end of 2017 for data on cancer incidence and in 2019 for data on the vital status. Cox proportional hazard model with time-varying exposure was used to assess the association. RESULTS: By the end of the follow-up period, 230,783 upper GI cancer cases and 99,348 upper GI cancer deaths were recorded. Negative gastric cancer screening was significantly associated with a lower risk of upper GI cancer in both UGIS (adjusted hazard ratio [aHR] = 0.81, 95% CI = 0.80-0.82) and upper endoscopy (aHR = 0.67, 95% CI = 0.67-0.68) groups. The HRs for upper GI mortality were 0.55 (95% CI = 0.54-0.56) and 0.21 (95% CI = 0.21-0.22) for the UGIS and upper endoscopy groups, respectively. The most significant reductions in the risk of upper GI cancer (UGIS: aHR = 0.76, 95% CI = 0.74-0.77; upper endoscopy: aHR = 0.60, 95% CI = 0.59-0.61) and death (UGIS: aHR = 0.54, 95% CI = 0.52-0.55; upper endoscopy: aHR = 0.19, 95% CI = 0.19-0.20) were observed among individual aged 60-69 years. CONCLUSION: Negative screening cases, especially in upper endoscopy of the KNCSP, were associated with an overall reduction in the risk of and mortality from upper GI cancer.
Subject(s)
Gastrointestinal Neoplasms , Stomach Neoplasms , Male , Humans , Female , Stomach Neoplasms/diagnosis , Stomach Neoplasms/epidemiology , Retrospective Studies , Early Detection of Cancer/methods , Gastrointestinal Neoplasms/diagnosis , Gastrointestinal Neoplasms/epidemiology , Republic of Korea/epidemiology , Endoscopy, GastrointestinalABSTRACT
Droplet-based microfluidic technology is a powerful tool for single-cell cultivation and rapid isolation of bacteria, yeasts and algae. However, it has been of limited use for studies of filamentous fungi due to the fast growth of their branched hyphae. The long regeneration time for fungal protoplasts and low-throughput screening methods are inherent problems for current genetic transformation techniques. Therefore, we have developed a novel droplet-based method for the filamentous fungus Trichoderma reesei expressing green fluorescent protein (GFP) as a marker. This approach presented several outstanding advantages over the traditional transformation method, including a 7-fold reduction in time for T. reesei protoplast regeneration, an 8-fold increase in regeneration frequency, and a screening speed of up to 8,000 droplets min-1. In this study, we encapsulated and incubated the gfp-transformed T. reesei protoplasts in droplets for 24 h, screened the droplets in a high-throughput assay, and eventually collected a transformant library with over 96 % of the candidates transformed with the marker gene. This versatile approach should make fungi more amenable to genetic manipulation and encourage strain improvements for industrial applications.
Subject(s)
Trichoderma , Trichoderma/genetics , Trichoderma/metabolism , Microfluidics , Gene Library , Green Fluorescent Proteins/genetics , Green Fluorescent Proteins/metabolism , Fungi/geneticsABSTRACT
OBJECTIVES: This study investigated the effect of mammography screening on the long-term survival of breast cancer (BC) patients aged 40 years or older according to their screening history and duration since screening. METHODS: The study cohort was organized from 3 nationwide databases of the Korean National Cancer Screening Program, the Korean Central Cancer Registry, and death certificates. We included 24,387 women diagnosed with invasive BC or ductal carcinoma in situ in 2008 and 2009 and followed up until December 31, 2019. Cox proportional-hazards regression was used to investigate the effect of BC screening on the risk of death. RESULTS: Overall, 20,916 of 24,387 patients (85.8%) were alive at the end of the follow-up period (median: 10.5 years). The long-term survival rate was significantly lower in the never-screened group (80.3%) than in the screened group (88.9%) (p<0.001). A 35% reduction in the risk of BC death (hazard ratio [HR], 0.65; 95% confidence interval [CI], 0.60 to 0.70) from screening was observed. A subgroup analysis according to the cancer stage showed 62%, 36%, and 24% lower risks of BC death for the localized stage, regional stage, and distant stage, respectively. Women aged 40-49 years received the least benefit from BC screening (HR, 0.71; 95% CI, 0.62 to 0.81). CONCLUSIONS: Mammography screening was effective in reducing the risk of BC-specific death in Asian women across all cancer stages. However, this effect was relatively small among women in their 40s, suggesting that more detailed and specialized screening strategies are needed for that age group.
Subject(s)
Breast Neoplasms , Humans , Female , Early Detection of Cancer , Mammography/methods , Proportional Hazards Models , Mass Screening , Republic of Korea/epidemiologyABSTRACT
OBJECTIVES: This study aimed to investigate the effect of cervical cancer screening by Papanicolaou (Pap) smears on the long-term survival of cervical cancer patients. METHODS: We constructed a retrospective cohort of 14,903 women diagnosed with invasive cancer or carcinoma in situ in 2008 and 2009 and followed up until December 31, 2019, by using individual-level data from 3 national databases of the Korean National Cancer Screening Program, the Korean Central Cancer Registry, and death certificates. Cox proportional-hazards regression was used to investigate the effect of cervical cancer screening on mortality. RESULTS: In total, 12,987 out of 14,867 patients (87.4%) were alive at the end of the follow-up period (median: 10.5 years). Screened patients had a 38% lower risk of cervical cancer death than never-screened patients (hazard ratio [HR], 0.62; 95% confidence interval [CI], 0.54 to 0.70). Screening was associated with 59% and 35% lower risks of death, respectively, in screened patients with localized and regional stages. Furthermore, lower HRs among women who received screening were observed in all age groups, especially women aged 50-59 years (HR, 0.54; 95% CI, 0.42 to 0.69). The lowest HR for cervical cancer death was reported among patients screened within the past 2 years (HR, 0.54; 95% CI, 0.47 to 0.63), and the HRs increased with increasing time intervals. CONCLUSIONS: Pap smear screening significantly reduced the risk of cervical cancer-specific death in Korean women across all cancer stages.
Subject(s)
Papanicolaou Test , Uterine Cervical Neoplasms , Humans , Female , Uterine Cervical Neoplasms/prevention & control , Vaginal Smears , Cohort Studies , Retrospective Studies , Early Detection of Cancer , Mass Screening , Republic of Korea/epidemiologyABSTRACT
BACKGROUND: Gastric cancer (GC) is the most common cancer type in Korea. Korean National Cancer Screening Program (KNCSP) offer either upper gastrointestinal series (UGIS) or upper endoscopy biennially for adults aged ≥ 40. This study aimed to investigate the effect of cancer screening program on the long-term survival among GC patients. METHODS: A nationwide population-based cohort was constructed based on three national databases. Overall, 46,701 GC patients diagnosed in 2008 and 2009 were included in our final analysis, and they were followed-up until the end of 2019. Survival curves were estimated using the Kaplan-Meier analysis with the log-rank test. Cox proportional-hazards regression analysis was used to report the hazard ratios (HRs) with 95% confidence intervals. RESULTS: A total of 18,614/46,701 (39.9%) patients died during the median follow-up time of 10.5 years. The survival rate was higher among screened patients (65.8%) than never-screened patients (49.1%). Screened patients had 53% (HR, 0.47; 95% CI 0.45-0.48) lower risk of death from GC. The HRs of GC-specific mortality was lower in upper endoscopy group (HR = 0.36; 95% CI = 0.34-0.37) compared with UGIS (HR = 0.69; 95% CI = 0.67-0.73). Screened patients within 2 years prior to cancer diagnosis had a 35% reduction in risk of GC death. The figure decline to approximately 19% among patients with interval time since last screening of > 3 years. CONCLUSIONS: Our findings emphasized the positive effects of GC screening on long-term GC patient survival. Also, patients screened by upper endoscopy or within 2 years before diagnosis had the best survival outcomes.
Subject(s)
Early Detection of Cancer , Stomach Neoplasms , Adult , Early Detection of Cancer/methods , Gastroscopy , Humans , Mass Screening/methods , Republic of Korea/epidemiology , Stomach Neoplasms/diagnosisABSTRACT
The Korea National Cancer Screening Program (KNCSP) provides fecal immunochemical test-based colorectal cancer (CRC) screening for people aged ≥50 years. Our study aimed to investigate the long-term survival effects of CRC screening based on screening history and interval time since screening. The study cohort was obtained by linking three national databases, namely the Korea Central Cancer Registry, KNCSP database and Death Certificate. We included 32 509 CRC patients diagnosed in 2008 to 2009, who underwent CRC screening via the KNCSP between 2004 and 2009. The patients were followed-up until 2019, and their survival was assessed according to their CRC screening history. Cox proportional hazards regression was used to compare time to deaths among CRC patients according to CRC screening history, after adjusting for covariates. Of the 32 509 patients, 20 022 (61.5%) patients were alive by the end of 2019. Long-term survival was significantly higher among screened patients (68.2%) than nonscreened (57.2%) individuals. Compared to never-screened patients, the hazard ratio (HR) for CRC-specific death in screened patients was 0.77 (95% CI%, 0.73-0.80). Lowest HR was observed in screened, localized CRC patients (HR, 0.48; 95% CI, 0.42-0.56); HR for CRC-specific death was the lowest in patients screened within 12 months of diagnosis (HR, 0.70; 95% CI, 0.66-0.74), following which, the HRs increased with increasing time interval. CRC screening was positively associated with favorable prognosis in CRC patients aged 50 to 79 years. The effects on long-term survival according to interval time was the best among individuals screened within 1 year before diagnosis.
Subject(s)
Colorectal Neoplasms , Early Detection of Cancer , Colonoscopy/methods , Colorectal Neoplasms/diagnosis , Early Detection of Cancer/methods , Humans , Mass Screening , Occult BloodABSTRACT
OBJECTIVES: This study aimed to validate a simple risk assessment tool for estimating the advanced colorectal neoplasia (ACN) risk at colonoscopy screenings and potential factors relevant for implementing this tool in the Korean population. METHODS: Our study analyzed data from the Cancer Screenee Cohort Study conducted by the National Cancer Center in Korea. The risk level was assessed using the Asia Pacific Colorectal Screening (APCS) score developed by the Asia-Pacific Working Group on Colorectal Cancer. Logistic regression models were used to examine the associations between colorectal-related outcomes and the risk level by APCS score. The discriminatory performance of the APCS score for various colorectal-related outcomes was assessed using C-statistics. RESULTS: In 12,520 individuals, 317 ACN cases and 4,528 adenoma cases were found. The APCS tool successfully classified the study population into different risk groups, and significant differences in the ACN rate and other outcomes were observed. The APCS score demonstrated acceptable discrimination capability with area under the curve values ranging from 0.62 to 0.65 for various outcomes. The results of the multivariate logistic regression model revealed that the high-risk group had a 3.1-fold higher risk of ACN (95% confidence interval, 2.08 to 4.67) than the average-risk group. Body mass index (BMI) was identified as a significant predictor of ACN in both multivariate and subgroup analyses. CONCLUSIONS: Our study highlighted significant differences in colorectal-related screening outcomes by colorectal risk level measured using the APCS score, and BMI could be used to improve the discriminatory capability of the APCS score.
Subject(s)
Colorectal Neoplasms , Early Detection of Cancer , Asia , Cohort Studies , Colorectal Neoplasms/diagnosis , Colorectal Neoplasms/epidemiology , Humans , Mass Screening , Republic of Korea/epidemiology , Risk Assessment , Risk Factors , SmokingABSTRACT
BACKGROUND: The Korea National Cancer Screening Program currently provides screening for colorectal cancer (CRC) for adults older than 50 years with no upper age limit. In general, people are likely to only pay attention to the benefits of cancer screening and to neglect its risks. Most consider the benefits of cancer screening as being far greater than the risks and are unaware that any potential benefits and harms can vary with age. AIM: To report acceptance of an upper age limit for CRC screening and factors associated therewith among cancer-free individuals in Korea. METHODS: The present study analyzed data from the Korea National Cancer Screening Survey 2017, a nationally representative random sample of 4500 Korean individuals targeted for screening for the five most common types of cancer. A total of 1922 participants were included in the final analysis. The baseline characteristics of the study population are presented as unweighted numbers and weighted proportions. Both univariate and multivariate logistic regression models were developed to examine factors related with acceptance of an upper age limit for CRC screening; subgroup analysis was also applied. RESULTS: About 80% (1554/1922) of the respondents agreed that CRC screening should not be offered for individuals older than 80 years. Specifically, those who had never been screened for CRC had the highest acceptance rate (91%). Overall, screening history for CRC [screened by both fecal occult blood test and colonoscopy, adjusted odds ratio (aOR) = 0.33, 95%CI: 0.22-0.50] and other cancers (aOR = 0.55, 95%CI: 0.34-0.87), as well as a family history of cancer (aOR = 0.66, 95%CI: 0.50-0.87), were negatively associated with acceptance of an upper age limit for CRC screening. In contrast, metropolitan residents (aOR = 1.86, 95%CI: 1.29-2.68) and people who exercised regularly (aOR = 1.42, 95%CI: 1.07-1.89) were more likely to accept an upper age limit. After subgrouping, we found gender, marital status, and lifetime smoking history among never-screened individuals and residential region, family history of cancer, and physical activity among never-screened individuals to be associated with acceptance of an upper age limit. CONCLUSION: This study describes acceptance of an upper age limit for CRC screening and factors associated with it, and provides perspectives that should be considered, in addition to scientific evidence, when developing population-based cancer screening policies and programs.
Subject(s)
Colorectal Neoplasms , Early Detection of Cancer , Patient Acceptance of Health Care , Adult , Aged, 80 and over , Colonoscopy , Colorectal Neoplasms/diagnosis , Colorectal Neoplasms/epidemiology , Female , Humans , Male , Mass Screening , Occult Blood , Republic of Korea/epidemiologyABSTRACT
Oligomerization of amyloid beta (Aß) peptides has been considered as the crucially causative agent in the development of Alzheimer's disease. Etersalate, a nonsteroidal anti-inflammatory oral drug (United State Food and Drug Administration-Unique Ingredient Identifier: 653GN04T2G) was previously suggested to bind well to proto-fibrils of Aß peptides in silico. Here, the effect of etersalate on the oligomerization of soluble Aß16-22 hexamer (6Aß16-22) were extensively investigated using temperature replica exchange molecular dynamics (REMD) simulations over ~16.8 µs in total for 48 replicas (350 ns per replica). The results reveal that etersalate can enter the inner space or bind on the surface of 6Aß16-22 conformations, which destabilizes the hexamer. Etersalate was predicted to able to cross the blood brain barrier using prediction of absorption, distribution, metabolism, and excretion-toxicity (preADMET) tools. Overall, although the investigation was performed with the low concentration of trial inhibitor, the obtained results indicate that etersalate is a potential drug candidate for AD through inhibiting formation of Aß oligomers with the average binding free energy of -11.7 kcal/mol.
Subject(s)
Amyloid beta-Peptides/metabolism , Anti-Inflammatory Agents, Non-Steroidal/pharmacology , Benzoates/pharmacology , Blood-Brain Barrier/metabolism , Computer Simulation , HumansABSTRACT
Breast cancer is the most common cancer in women in the USA, with the lifetime incidence of 1 in 8 women. Dermatomyositis (DM) is an uncommon idiopathic inflammatory myopathy that can manifest as a paraneoplastic syndrome of an underlying malignancy. Here, we report a case of a patient who presented with breast cancer and DM symptoms. The patient's rash and muscle weakness progressed during the workup of her breast cancer, while she was already started on medical treatment of these symptoms with oral prednisone. Her cutaneous and musculoskeletal improved dramatically following the treatment of her breast cancer. Our case report describes the rapid progression and regression of her symptoms emphasizing the benefit of early diagnosis and treatment of DM as well as the underlying breast cancer.
ABSTRACT
The equilibrium behavior of ellipsoidal Janus nanoparticles adsorbed at spherical oil/water interfaces was investigated using dissipative particle dynamics simulations. Several phenomena were documented that were not observed on similar simulations for planar oil/water interfaces. The nanoparticles were found to yield isotropic, radial nematic phases, and axial nematic domains, depending on the nanoparticle characteristics (aspect ratio and surface chemistry), particle density at the interface, and droplet properties (curvature of the interface, and surprisingly, liquid type). When adsorbed on water droplets, the nanoparticles with high aspect ratio and few nonpolar beads on their surface can show two preferred orientation angles. Only one equilibrium orientation was found for such nanoparticles adsorbed on oil droplets. These observations might help explain a discrepancy previously reported between experimental and simulation results concerning the preferential orientation of particles at liquid-liquid interfaces. Different driving forces are responsible for the phenomena just summarized, including nanoparticle-nanoparticle and nanoparticle-solvent interactions, nanoparticle density at the interface, and droplet curvature via the Laplace pressure. The simulation results we present could be useful for engineering Pickering emulsions toward practical applications, and perhaps also for guiding new technologies for material synthesis.
ABSTRACT
BACKGROUND: Granulomatous mastitis is an uncommon chronic inflammatory breast condition that is characterized by granulomatous inflammation. Granulomatous mastitis presents a challenging clinical scenario, because it can mimic carcinoma. The etiology and optimal treatment remain unclear. We report our experience with granulomatous mastitis patients who presented to our clinic within the past 2 years and describe their response to our treatment modalities. METHODS: Our clinic records were reviewed for the diagnosis of granulomatous mastitis. Charts were used to collect clinical data, patients were reinter viewed, and physicians completed detailed reports on their management of these cases. All cases were diagnosed with granulomatous mastitis based on histological findings and by ruling out other etiologies. RESULTS: Twenty-four patients were identified. The mean age was 34 years. Fifty-three percent of our patients emigrated from Mexico. Most patients were treated with prednisone and/or methotrexate with overall response rate greater than 80 %. Cases that failed to improve were treated with other modalities, including antituberculosis drugs. CONCLUSIONS: Granulomatous mastitis remains a difficult entity to diagnose and to treat. The clinical course of patients often is prolonged. Exclusion of other causes of granulomatous conditions is essential before initiating anti-inflammatory treatment.
Subject(s)
Anti-Inflammatory Agents/therapeutic use , Antitubercular Agents/therapeutic use , Granulomatous Mastitis/diagnosis , Granulomatous Mastitis/drug therapy , Methotrexate/therapeutic use , Prednisone/therapeutic use , Adult , Diagnosis, Differential , Drug Therapy, Combination , Female , Follow-Up Studies , Granulomatous Mastitis/therapy , Hospitals, Public , Humans , Mastectomy , Middle Aged , New York , Retrospective Studies , Suction , Treatment OutcomeABSTRACT
The equilibrium behavior of ellipsoidal Janus nanoparticles at water-oil interfaces was investigated using dissipative particle dynamics simulations. It was found that the orientation of the nanoparticles with respect to the interface depends on nanoparticle aspect ratio, on the amount of polar vs nonpolar surface groups, and on the interactions between the nanoparticles surface groups and aqueous and nonaqueous solvents. The changes in nanoparticle orientation are not always monotonic, probably because of a competition between different driving forces. For nanoparticles of high aspect ratio, steric effects seem to cause an isotropic-to-nematic phase transition as the surface coverage increases. It was observed that at a sufficiently high surface coverage the nanoparticles are most effective at reducing the interfacial tension when they lay with their longer axis parallel to the interface. The simulation results presented could be useful for the design of Pickering emulsions.
Subject(s)
Nanoparticles/chemistry , Oils/chemistry , Water/chemistry , Adsorption , Molecular Dynamics Simulation , Surface Properties , TemperatureABSTRACT
Dissipative particle dynamics simulations are performed to study the structural and dynamical properties of various systems of nanoparticles accumulated at the water/oil interface. Homogeneous and Janus nanoparticles with different surface compositions are studied. For all nanoparticles, as the surface density increases, a transition from a liquidlike to a solidlike state is observed, as expected. At a high density of nanoparticles, hexagonal structures emerge and the nanoparticles' self-diffusion coefficient decreases because of caging effects. Similar results are observed for nanoparticles with different surface chemistry. Because different nanoparticles have different contact angles at the water/oil interface, the results obtained for systems containing mixed nanoparticles are more interesting. For example, our results show that the self-diffusion coefficient is not a monotonic function of the system composition, caused by the complex relation between hydrodynamic interactions and effective nanoparticle-nanoparticle interactions.
Subject(s)
Nanoparticles , Oils/chemistry , Water/chemistry , Diffusion , Molecular StructureABSTRACT
The diffusiophoresis of a rigid, nonuniformly charged spherical particle in an electrolyte solution is analyzed theoretically focusing on the influences of the thickness of double layer, the surface charge distribution, the effect of electrophoresis, and the effect of double-layer polarization. We show that the nonuniform charge distribution on the particle surface yields complicated effect of double-layer polarization, leading to interesting diffusiophoretic behaviors. For example, if the sign of the middle part of the particle is different from that of its left- and right-hand parts, then depending upon the charge density and the fraction of the middle part, the particle can move either to the high-concentration side or to the low-concentration side. Both the diffusiophoretic velocity and its direction can be manipulated by the distribution of the surface charge density. In particular, if the electrophoresis effect is significant, then those properties are governed by the averaged surface charge density of the particle. A dipolelike particle, where its left- (right-) hand half is negatively (positively) charged, always migrates toward the low-concentration (left-hand) side, that is, it has a negative diffusiophoretic velocity. In addition, that diffusiophoretic velocity has a negative local minimum as the thickness of double layer varies.