Effects of the chain length of nonaromatic epoxy resins on thermomechanical and optical properties: experiments, and ab initio and molecular dynamics simulations.

Epoxy resin has been extensively used in the field of advanced electronic materials as an adhesive and encapsulant owing to its excellent material properties. However, recently, there has been a demand for further improvement in heat resistance, high transparency, environmental resistance, and enhanced handling properties for high-brightness light-emitting diodes. Conventional aromatic epoxy resins lack light resistance; therefore, a colorless and transparent epoxy resin without aromatic rings is desirable. In this study, tris(2,3-epoxypropyl) isocyanurate (TEPIC) was used as a nonaromatic epoxy resin, and three types of TEPIC with different side-chain lengths were prepared. The ultraviolet (UV)-visible absorption properties of TEPIC were evaluated using time-dependent density functional theory, and the practicality of the numerical prediction of light resistance was verified. TEPIC yields a UV absorbance spectrum with a lower intensity than those of conventional aromatic epoxy resins, suggesting that TEPIC is expected to have high light resistance. In addition, their thermomechanical properties and the influence of molecular structure were evaluated using both molecular dynamics (MD) simulations and experiments. The MD simulation and experimental results were in good agreement, indicating that the long side chains of TEPIC suppress triaxial deformation-induced failure and improve ductility instead of decreasing strength and stiffness. In addition, the longer side chains form a dense molecular structure with less free volume. These results indicate that numerical approaches can be used to predict various properties of epoxy resins and interpret them from the molecular structure. Accordingly, these approaches can be used to aid the material development process.

Determination of interaction parameters in a bottom-up approach employed in reactive dissipative particle dynamics simulations for thermosetting polymers.

The limitations in previous dissipative particle dynamics (DPD) studies confined simulations to a narrow resin range. This study refines DPD parameter calculation methodology, extending its application to diverse polymer materials. Using a bottom-up approach with molecular dynamics (MD) simulations, we evaluated solubility parameters and bead number density governing nonbonded interactions via the Flory-Huggins parameter and covalent-bonded interactions. Two solubility parameter methods, Hildebrand and Krevelen-Hoftyzer, were compared for DPD simulations. The Hildebrand method, utilizing MD simulations, demonstrates higher consistency and broader applicability in determining solubility parameters for all DPD particles. The DPD/MD curing reaction process was examined in three epoxy systems: DGEBA/4,4'-DDS, DGEBA/MPDA and DGEBA/DETA. Calculations for the curing profile, gelation point, radial distribution function and branch ratio were performed. Compared to MD data for DGEBA/4,4'-DDS, the maximum deviation in secondary reactions between epoxy and amine groups according to DPD simulations with Krevelen-Hoftyzer was 14.8%, while with the Hildebrand method, it was 1.7%. The accuracy of the DPD curing reaction in reproducing the structural properties verifies its expanded application to general polymeric material simulations. The proposed curing DPD simulations, with a short run time and minimal computational resources, contributes to high-throughput screening for optimal resins and investigates mesoscopic inhomogeneous structures in large resin systems.

Effect of inorganic material surface chemistry on structures and fracture behaviours of epoxy resin.

The mechanisms underlying the influence of the surface chemistry of inorganic materials on polymer structures and fracture behaviours near adhesive interfaces are not fully understood. This study demonstrates the first clear and direct evidence that molecular surface segregation and cross-linking of epoxy resin are driven by intermolecular forces at the inorganic surfaces alone, which can be linked directly to adhesive failure mechanisms. We prepare adhesive interfaces between epoxy resin and silicon substrates with varying surface chemistries (OH and H terminations) with a smoothness below 1 nm, which have different adhesive strengths by ~13 %. The epoxy resins within sub-nanometre distance from the surfaces with different chemistries exhibit distinct amine-to-epoxy ratios, cross-linked network structures, and adhesion energies. The OH- and H-terminated interfaces exhibit cohesive failure and interfacial delamination, respectively. The substrate surface chemistry impacts the cross-linked structures of the epoxy resins within several nanometres of the interfaces and the adsorption structures of molecules at the interfaces, which result in different fracture behaviours and adhesive strengths.

Dissipative Particle Dynamics Simulation for Reaction-Induced Phase Separation of Thermoset/Thermoplastic Blends.

Reaction-induced phase separation occurs during the curing reaction when a thermoplastic resin is dissolved in a thermoset resin, which enables toughening of the thermoset resin. As resin properties vary significantly depending on the morphology of the phase-separated structure, controlling the morphology formation is of critical importance. Reaction-induced phase separation is a phenomenon that ranges from the chemical reaction scale to the mesoscale dynamics of polymer molecules. In this study, we performed curing simulations using dissipative particle dynamics (DPD) coupled with a reaction model to reproduce reaction-induced phase separation. The curing reaction properties of the thermoset resin were determined by ab initio quantum chemical calculations, and the DPD parameters were determined by all-atom molecular dynamics simulations. This enabled mesoscopic simulations, including reactions that reflect the intrinsic material properties. The effects of the thermoplastic resin concentration, molecular weight, and curing conditions on the phase-separation morphology were evaluated, and the cure shrinkage and stiffness of each cured resin were confirmed to be consistent with the experimental trends. Furthermore, the local strain field under tensile deformation was visualized, and the inhomogeneous strain field caused by the phase-separated structures of two resins with different stiffnesses was revealed. These results can aid in understanding the toughening properties of thermoplastic additives at the molecular level.

In-situ shearing process observation system for soft materials via transmission electron microscopy.

We developed an in-situ shear test system suitable for transmission electron microscopy (TEM) observations, which enabled us to examine the shear deformation behaviours inside soft materials at nanoscale resolutions. This study was conducted on a nanoparticle-filled rubber to investigate its nanoscale deformation behaviour under a large shear strain. First, the shear deformation process of a large area in the specimen was accurately examined and proven to exhibit an almost perfect simple shear. At the nanoscale, voids grew along the maximum principal strain during shear deformation. In addition, the nanoscale regions with rubber and silica aggregates exhibited deformation behaviours similar to the global shear deformation of the specimen. Although the silica aggregates exhibited displacement along the shearing directions, rotational motions were also observed owing to the torque generated by the local shear stress. This in-situ shear deformation system for TEM enabled us to understand the nanoscale origins of the mechanical properties of soft materials, particularly polymer composites. Graphical Abstract.

Uncovering the Mechanism of Size Effect on the Thermomechanical Properties of Highly Cross-Linked Epoxy Resins.

Epoxy resins are widely used as matrix resins, especially for carbon-fiber-reinforced plastic, due to their outstanding physical and mechanical properties. To date, most research into cross-linking processes using simulation has considered only a distance-based criterion to judge the probability of reaction. In this work, a new algorithm was developed for use with the large-scale atomic/molecular massively parallel simulator (LAMMPS) simulation package to study the cross-linking process; this new approach combines both a distance-based criterion and several kinetic criteria to identify whether the reaction has occurred. Using this simulation framework, we investigated the effect of model size on predicted thermomechanical properties of three different structural systems: diglycidyl ether of bisphenol A (DGEBA)/4,4'-diaminodiphenyl sulfone (4,4'-DDS), DGEBA/diethylenetriamine (DETA), and tetraglycidyl diaminodiphenylmethane (TGDDM)/4,4'-DDS. Derived values of gel point, volume shrinkage, and cross-linked resin density were found to be insensitive to model size in these three systems. Other thermomechanical properties, i.e., glass-transition temperature, Young's modulus, and yield stress, were found to reach stable values for systems larger than ∼40 000 atoms for both DGEBA/4,4'-DDS and DGEBA/DETA. However, these same properties modeled for TGDDM/4,4'-DDS did not stabilize until the system size reached 50 000 atoms. Our results provide general guidelines for simulation system size and procedures to more accurately predict the thermomechanical properties of epoxy resins.

Thermoset resin curing simulation using quantum-chemical reaction path calculation and dissipative particle dynamics.

Thermoset resin, which is commonly used as a matrix in carbon-fiber-reinforced plastic, requires curing procedures. We propose a curing simulation technique involving a dissipative particle dynamics (DPD) simulation, which can simulate a larger system and longer time period than those of conventional all-atom molecular dynamics (AA-MD) simulations. The proposed curing DPD simulation can represent the thermoset resin exothermic reaction process precisely by considering each reactivity according to the reaction types calculated via quantum-chemical reaction path calculations. The cure reaction process given by the curing DPD simulation agrees well with that given by a conventional curing AA-MD simulation, but with run-time and computational-resource reductions of 1/480 and 1/10 times, respectively. We also conduct reverse mapping, through which the AA-MD system can be reconstructed from the DPD system, to evaluate the structural and thermomechanical properties. The X-ray diffraction pattern and thermomechanical properties of the reconstructed system agree well with those of the systems derived from the curing AA-MD simulation and experimental setup. Therefore, a cured-resin AA-MD system can be obtained from a curing DPD simulation at an extremely low computational cost, and the thermomechanical properties can be evaluated precisely using this system. The proposed curing simulation technique can be applied in high-throughput screening for better materials properties and in large system calculations.

Cross-Plane and In-Plane Heat Conductions in Layer-by-Layer Membrane: Molecular Dynamics Study.

A material with anisotropic heat conduction characteristics, which is determined by molecular scale structure, provides a way of controlling heat flow in nanoscale spaces. As such, here, we consider layer-by-layer (LbL) membranes, which are an electrostatic assembly of polyelectrolyte multilayers and are expected to have different heat conduction characteristics between cross-plane and in-plane directions. We constructed models of a poly(acrylic acid)/polyethylenimine (PAA/PEI) LbL membrane sandwiched by charged solid walls and investigated their anisotropic heat conduction using molecular dynamics simulations. In the cross-plane direction, the thermal boundary resistance between the solid wall and the LbL membrane and that between the constituent PAA and PEI layers decrease with increasing degree of ionization (solid surface charge density and the number of electric charges per PAA/PEI molecule). When the degree of ionization is low, the cross-plane thermal conductivity of a constituent layer is higher than that of the bulk state. As the degree of ionization increases, however, the cross-plane thermal conductivity of PAA, a linear polymer, decreases because of the increase in the number of in-plane oriented polymer chains. In the in-plane direction, we investigated the heat conduction of each layer and found the enhancement of effective in-plane thermal conductivity again due to the in-plane oriented chain alignment. The heat conduction in the LbL membrane is three-dimensionally enhanced compared to those in the bulk states of the constituent polymers because of the electrostatic interactions in the cross-plane direction and the molecular alignment in the in-plane direction.

Molecular dynamics investigation of surface roughness scale effect on interfacial thermal conductance at solid-liquid interfaces.

Non-equilibrium molecular dynamics simulations were conducted for solid-liquid-solid systems with nanometer scale grooved surfaces and an induced heat flux for a wide range of topology and solid-liquid interaction conditions to investigate the mechanism of solid-liquid heat transfer, which is the first work of such extensive detail done about the nanoscale roughness effect on heat transfer properties. Single-atom molecules were used for liquid, and the solid-liquid interaction was varied from superhydrophobic to superhydrophilic, while the groove scale was varied from single atom to several nanometers, while keeping the surface area twice that of a flat surface. Both Wenzel and Cassie wetting regimes with a clear transition point were observed due to the capillary effect inside larger grooves that were more than 5 liquid molecule diameters, while such transition was not observed at smaller scales. At the hydrophobic state, large scale grooves had lower interfacial thermal conductance (ITC) due to the Cassie regime, i.e., having unfilled grooves, while at the hydrophilic state, grooved surfaces had ITC about twice that of a flat surface, indicating an extended heat transfer surface effect regardless of the groove scale. At the superhydrophilic state, crystallization of liquid at the surface occurred, and the packing of liquid molecules had a substantial effect on ITC regardless of the groove scale. Finally, both potential energy of solid-liquid interaction and work of solid-liquid adhesion were calculated and were shown to be in similar relations to ITC for all groove scales, except for the smallest single-atom scale grooves, due to a different heat transfer mechanism.

The serum level of soluble CD26/dipeptidyl peptidase 4 increases in response to acute hyperglycemia after an oral glucose load in healthy subjects: association with high-molecular weight adiponectin and hepatic enzymes.

A soluble form of CD26/dipeptidyl peptidase 4 (sCD26/DPP4) is found in serum and it has DPP4 enzymatic activity. We investigated whether the serum level of sCD26/DPP4 was influenced by the oral glucose tolerance test (OGTT) in healthy subjects. The serum sCD26/DPP4 level increased significantly from 824.5 ng/mL (interquartile range, from 699.0 to 1050 ng/mL) at baseline to a peak of 985.0 ng/mL (interquartile range, from 796.5 to 1215 ng/mL) during the OGTT (P < 0.0001). The peak sCD26/DPP4 level correlated positively with the baseline age and body mass index, and fasting plasma glucose (FPG), homeostasis model assessment of insulin resistance (HOMA-IR), triglycerides (TG), alanine aminotransferase, and γ-glutamyl transpeptidase (GGT) levels whereas it correlated negatively with high-density lipoprotein (HDL) cholesterol and the serum levels of total and high-molecular weight (HMW) adiponectin. Stepwise regression analysis was done with forward selection of variables, including age, FPG, HOMA-IR, TG, HDL cholesterol, uric acid, GGT, C-reactive protein, and HMW adiponectin. In a model that explained 57.5% of the variation of the peak sCD26/DPP4 level, GGT (ß = 0.382, P = 0.007) and HOMA-IR (ß = 0.307, P = 0.034) were independent determinants of the peak serum level of sCD26/DPP4. Serum HMW adiponectin decreased significantly from 4.43 µg/mL (interquartile range, from 2.80 to 6.65 µg/mL) at baseline to 4.17 µg/mL (interquartile range, from 2.48 to 6.96 µg/mL) 120 minutes after the oral glucose load (P < 0.0001). The baseline serum level of sCD26/DPP4 showed a significant negative correlation with the percent change of HMW adiponectin during the OGTT. In conclusion, the serum level of sCD26/DPP4 increased acutely after an oral glucose load in apparently healthy subjects. The abrupt increase of serum sCD26/DPP4 after a glucose load may be a marker of insulin resistance that could come from liver or muscle.

A case of myeloma with hypercalcemia caused by high serum concentrations of both parathyroid hormone-related peptide (PTHrP) and macrophage inflammatory protein-1α (MIP-1α).

A 62-year-old woman was admitted with dry mouth, general fatigue, and severe back pain. Biochemistry examination showed extreme hypercalcemia (21.2 mg/dL). Bone marrow examination was negative, but needle biopsy of a metastatic lung tumor revealed abnormal plasma cells; thus, multiple myeloma stage III-A was finally diagnosed. Serum concentrations of both parathyroid hormone-related peptide (PTHrP) and macrophage inflammatory protein-1α (MIP-1α) were markedly elevated (PTHrP 7.2 pmol/L, normal <1.1 pmol/L; MIP-1α 84.9 pg/mL, normal <46.9 pg/mL). Her myeloma appeared to have simultaneously caused two mechanisms producing hypercalcemia: humoral hypercalcemia of malignancy (HHM) by PTHrP and local osteolytic hypercalcemia (LOH) by MIP-1α. Therefore, the combination of two calcium-modulating abnormalities likely aggravated her hypercalcemia.

Comparative study between high-dose fluvastatin and low-dose fluvastatin and ezetimibe with regard to the effect on endothelial function in diabetic patients.

It is well established that statins improve the prognosis of patients with coronary artery disease. However, it is still unclear whether the protective effects of statins relate to lipid lowering alone or whether other pleiotropic effects may contribute. Thus, we compared the endothelial function among two groups of diabetic patients treated with fluvastatin 60 mg (F60) or fluvastatin 20 mg combined with ezetimibe 10 mg (F20/E10). The endothelial function was evaluated by measuring flow-mediated vasodilatation (FMD) at baseline and follow-up at 10 weeks. Similar improvements in FMD were observed in the two groups. The reduction in low-density lipoprotein cholesterol (LDL-C) was less pronounced in the F60 group, compared with the F20/E10 group. A significant reduction in remnant-like lipoprotein particles cholesterol (RLP-C) was observed in the F20/E10 group, but not in the F60 group. A correlation between the observed reduction in LDL-C or RLP-C and the improvement in FMD was observed in F20/E10 group. These results suggest that high-dose fluvastatin might have pleiotropic effects of potential clinical benefit, and that the combination of ezetimibe with a reduced dose of fluvastatin may also significantly improve endothelial function with reduction of LDL-C and RLP-C.

Early recovery in hemodynamics after direct hemoperfusion with polymyxin B-immobilized fibers may predict mortality rate in patients with septic shock.

PURPOSE: This retrospective and observational study attempted to determine whether the rapid improvement in hemodynamic parameters and the subsequent discontinuation or decrease of catecholamine infusion shortly after direct hemoperfusion with polymyxin B-immobilized fibers (PMX) may be strong predictors of mortality in patients with septic shock. METHODS: Retrospectively, 46 patients were divided into two groups; those who survived more than 30 days after PMX (survival group, S group) and those who died within 30 days (nonsurvival group, NS group). Sequential Organ Failure Assessment (SOFA) scores, mean arterial pressure, catecholamine index (CAI), and vasopressor dependency index (VDI) were examined before and after PMX. The same parameters were examined on days 3, 4, 5, 6, 8, and 16 after PMX. RESULTS: CAI in the S group significantly decreased from 14.7 (95% CI, 10.3-19.1) at baseline to 6.4 (95% CI, 3.7-9.2; P < 0.001) at post-PMX, whereas a significant decrease in CAI was not observed in the NS group (23.1; 95% CI, 15.4-30.7 to 18.1; 95% CI, 11.6-24.7; P = 0.114). The significant decrease in VDI at post-PMX was observed both in the S group and in the NS group. If the cutoff point of VDI at post-PMX is 0.2, there is a significant difference in numbers of the S group (VDI ≥ 0.2, n = 24; VDI < 0.2, n = 2) and NS group (VDI ≥ 0.2, n = 8; VDI < 0.2, n = 20) using Fisher's exact test. CONCLUSIONS: We concluded that the early improvement in CAI and VDI shortly after PMX might be prognostic indicators for survival.

Effect of raloxifene on serum lipids for type 2 diabetic menopausal women with or without statin treatment.

OBJECTIVE: Our aim was to investigate the effect of 1-year treatment with raloxifene, a selective estrogen receptor modulator, on plasma lipid profiles in Japanese postmenopausal type 2 diabetic patients. SUBJECTS AND METHODS: A total of 43 Japanese women with postmenopausal osteoporosis and type 2 diabetes with serum low-density lipoprotein cholesterol (LDL-C) <3.59 mmol/l, serum triglyceride <1.68 mmol/l and serum high-density lipoprotein cholesterol (HDL-C) >1.03 mmol/l, who took 60 mg/day of raloxifene for 12 months, were enrolled. For analysis, they were divided into 2 groups: nonhyperlipidemia (n = 23) and hyperlipidemia treated with statin (n = 20). RESULTS: Raloxifene treatment significantly induced a mean reduction in serum LDL-C from 2.90 to 2.36 and 2.67 mmol/l in the nonhyperlipidemia and statin-treated group, respectively. However, the reduction ratio of serum LDL-C showed a significant difference in the nonhyperlipidemia group (17%) compared to the statin-treated group (7%; p = 0.03). Although serum HDL-C showed an increase in both groups (from 1.45 to 1.58 vs. from 1.40 to 1.47 mmol/l), the increase ratio of serum HDL-C was not significant between the two groups. Raloxifene administration showed 15% reduction in the nonhyperlipidemia group (p = 0.02) and 13% reduction in the statin-treated group (p = 0.02) of urinary N-telopeptide of type I collagen. No significant change in blood HbA(1c) was observed in either group. CONCLUSION: The administration of raloxifene to type 2 diabetic women showed favorable efficacy on serum lipid profiles, particularly in patients without statin treatment.

Effects of changeover from voglibose to acarbose on postprandial triglycerides in type 2 diabetes mellitus patients.

INTRODUCTION: In this study, we examined the effects of the alpha-glucosidase inhibitors acarbose and voglibose on postprandial plasma glucose and serum triglyceride levels in patients with type 2 diabetes mellitus. METHODS: Twenty-one Japanese patients with type 2 diabetes were enrolled in this study. Subjects had been treated with voglibose for at least 3 months. They underwent a 400 kcal balanced food meal tolerance test before and 8 weeks after the changeover from voglibose to acarbose. Subjects were divided into two groups: the first group (low-dose group; n=11) was changed over from 0.6 mg/day voglibose to 150 mg/day acarbose, and the other (high-dose group; n=10) from 0.9 mg/day voglibose to 300 mg/day acarbose. RESULTS: The increment rate of postprandial plasma glucose ([plasma glucose 2 hours after test meal - fasting glucose]/fasting glucose) decreased from 34.7%+/-23.9% to 25.0%+/-24.6% (P=0.13) in the low-dose group, and decreased significantly from 56.1%+/-53.1% to 31.5%+/-36.0% (P=0.03) in the high-dose group after changeover. However, there were no significant changes in blood glycated hemoglobin (HbA(1c)) levels before and after changeover in either group. The increment rate of postprandial serum triglyceride (TG) ([serum TG 2 hours after test meal - fasting TG]/fasting TG) decreased significantly only in the high-dose group (52.4%+/-60.0% to 24.3%+/-16.6%) (P=0.05). No significant changes in serum high-density lipoprotein cholesterol levels were observed in either group, whereas serum low-density lipoprotein cholesterol levels decreased significantly from 3.20+/-0.25 to 2.65+/-0.18 mmol/L (P=0.04), only in the high-dose group. CONCLUSIONS: In patients with type 2 diabetes our findings suggest that acarbose 300 mg/day is superior to voglibose 0.9 mg/day in improving postprandial hyperglycemia and hypertriglyceridemia.