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When confined in nanoscale domains, polymers generally encounter changes in their structural, thermodynamics and dynamics properties compared to those in the bulk, due to the high amount of polymer/wall interfaces and limited amount of matter. The present review specifically deals with the confinement of heterogeneous polymers (i.e. polymer blends and block copolymers) in rigid nanoscale domains (i.e. bearing non-deformable solid walls) where the processes of phase separation and self-assembly can be deeply affected. This review focuses on the innovative contributions of the last decade (2010-2020), giving a summary of the new insights and understanding gained in this period. We conclude this review by giving our view on the most thriving directions for this topic.
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Film-forming systems are highly relevant to the topical administration of active ingredients (AI) to the body. Enhanced contact with the skin can increase the efficacy of delivery and penetration during prolonged exposure. However, after the evaporation of volatile solvents to form a thin film, the distribution of the ingredient should remain homogenous in order to ensure the effectiveness of the formula. This is especially critical for the use of hydrophobic molecules that have poor solubility in hydrophilic films. In order to address this concern, hydroxyphenethyl esters (PHE) of Punica granatum seed oil were prepared as a nanosuspension stabilised by poloxamers (NanoPHE). NanoPHE was then added to a formulation containing polyvinyl alcohol (PVA) as a film forming agent, Glycerol as a plasticiser and an antimicrobial agent, SepicideTM HB. Despite their reliability, reference methods such as high-performance liquid chromatography are increasingly challenged due to the need for consumables and solvents, which is contrary to current concerns about green industry in the cosmetics field. Moreover, such methods fail to provide spatially resolved chemical information. In order to investigate the distribution of ingredients in the dried film, Confocal Raman imaging (CRI) coupled to Non-negatively Constrained Least Squares (NCLS) analysis was used. The reconstructed heat maps from a range of films containing systematically varying PHE concentrations highlighted the changes in spectral contribution from each of the ingredients. First, using NCLS scores it was demonstrated that the distributions of PVA, Glycerol, SepicideTM HB and PHE were homogenous, with respective relative standard deviations (RSD) of 3.33%, 2.48%, 2.72% and 6.27%. Second, the respective relationships between ingredient concentrations in the films and their Raman responses, and the spectral abundance were established. Finally, a model for absolute quantification for PHE was be constructed using the percentage of spectral abundance. The prepared %w/w concentrations regressed against predicted %w/w concentrations, displaying high correlation (R2 = 0.995), while the Root Mean Squared Error (0.0869% w/w PHE) confirmed the precision of the analysis. The mean percent relative error of 3.75% indicates the accuracy to which the concentration in dried films could be determined, further supporting the suitability of CRI for analysis of composite solid film matrix. Ultimately, it was demonstrated that nanoformulation of hydrophobic PHE provides homogenous distribution in PVA based film-forming systems independent of the concentration of NanoPHE used in the formula.
Asunto(s)
Cosméticos/química , Membranas Artificiales , Nanoestructuras , Aceites de Plantas/química , Granada (Fruta)/química , Semillas/química , Administración Tópica , Cosméticos/uso terapéutico , Evaluación de Medicamentos , Interacciones Hidrofóbicas e Hidrofílicas , Aceites de Plantas/uso terapéutico , Espectrometría Raman , SuspensionesRESUMEN
OBJECTIVE: Cosmetic films and patches are interesting forms to promote skin penetration of active ingredients as they ensure their long stay on the treated zone of the skin. Nevertheless, currently developed films and patches are most of all hydrophilic and are not adapted to the hydrophobic molecules. The aim of this study was to establish whether nanodispersion of fatty acid-based active cosmetic ingredients (ACI) could be a manner to introduce high concentrations of those ACI in hydrophilic films. METHODS: Punica granatum seed oil hydroxyphenethyl esters (PHE) constitute a commercialized lipolytic cosmetic ingredient obtained by enzymatic conjugation of tyrosol to long-chain fatty acids and to enhance its skin diffusion. Nanodispersions of PHE were prepared by a green emulsion-solvent evaporation process and dispersed in polyvinyl alcohol films. Raman imaging coupled to multivariate analysis was used to study the distribution of PHE in the films. RESULTS: Nanodispersions of PHE combined with antioxidant vitamin E and stabilized by Pluronic® F127 were successfully prepared. The nanodispersions show a spherical shape and a hydrodynamic diameter close to 100 nm. Raman images analysis with multivariate approaches showed a very homogeneous distribution of PHE nanodispersions in the films compared to free PHE introduced as an ethanol solution. CONCLUSION: Nanodispersions of hydrophobic fatty acid-based ingredients seem to be relevant method to introduce this type of ingredient in hydrophilic film matrix. The co-suspension with vitamin E limits their degradation in time.
OBJECTIF: Les films et patchs cosmétiques sont des formes intéressantes pour augmenter la pénétration cutanée des actifs cosmétiques car ils assurent une exposition prolongée de la zone de peau traitée ce qui favorise la diffusion. Néanmoins, les films et patchs actuellement développés sont majoritairement de nature hydrophile et ne sont pas adaptés aux molécules hydrophobes. Le but de cette étude est d'établir si la nanodispersion d'actifs cosmétiques à base d'acides gras peut être un moyen d'introduire des concentrations élevées de ces actifs dans des films hydrophiles. MÉTHODES: Les esters hydroxyphénéthyliques de l'huile de graines de grenade Punica granatum (PHE) sont commercialisés comme un agent lipolytique. Cet actif obtenu par conjugaison enzymatique du tyrosol à des acides gras à longue chaîne ce qui favorise sa pénétration cutanée. Des nanodispersions de PHE ont été préparées par un procédé d'émulsion- évaporation développé avec un solvant vert. Ces nanosystèmes sont ensuite dispersées dans des films d'alcool polyvinylique. L'imagerie Raman couplée à une méthode d'analyse statistique multivariée a été utilisée pour étudier la distribution des PHE dans les films. RÉSULTATS: Des nanodispersions de PHE associées à de la vitamine E antioxydante et stabilisées par Pluronic® F127 ont été préparées avec succès. Les nanodispersions présentent une forme sphérique et un diamètre hydrodynamique proche de 100 nm. L'analyse d'images Raman au moyen d'une approche multivariée a montré une distribution très homogène des nanodispersions dans les films par rapport aux PHE libres introduits sous forme de solution éthanolique. CONCLUSION: Les nanodispersions d'ingrédients hydrophobes à base d'acides gras semblent être une méthode pertinente pour introduire ce type d'ingrédient dans la matrice de film hydrophile. L'introduction de vitamine E dans les nanodispersion ralentit leur dégradation.
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Cosméticos/química , Ácidos Grasos/química , Nanotecnología , Interacciones Hidrofóbicas e Hidrofílicas , Granada (Fruta)/química , Espectrometría RamanRESUMEN
In this work, a water-soluble (hydrophilic) polymer was used to form a hydrophobic coating on silicon substrates (Si) in a two-step process comprising (i) the transformation of the polymer into an insoluble material and (ii) the structuring of this coating at nanometric and micrometric scales to achieve the desired hydrophobic behavior. Polyvinylpyrrolidone (PVP), a water-soluble commodity polymer, was crosslinked using benzophenone and UV irradiation to produce a water-insoluble PVP coating. The nanometric scale roughness of the coating was achieved by the addition of silica nanoparticles (NPs) in the coating. The micrometric scale roughness was achieved by forming vertical pillars of PVP/NP coating. To prepare these pillars, a perforated polystyrene (PS) template was filled with a PVP/NP suspension. Micrometer scale vertical pillars of PVP/silica NPs were produced by this method, which allowed us to tune the wettability of the surface, by combining the micrometric scale roughness of the pillars to the nanometric scale roughness provided by the nanoparticles at the surface. By adjusting the various experimental parameters, a hydrophobic PVP coating was prepared with a water contact angle of 110°, resulting in an improvement of more than 80% compared to the bare flat film with an equal amount of nanoparticles. This study paves the way for the development of a more simplified experimental approach, relying on a blend of polymers containing PVP and NPs, to form the micro/nano-structured PVP pillars directly after the deposition step and the selective etching of the sacrificial major phase.
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In this work, direct irradiation by a Ti:Sapphire (100 fs) femtosecond laser beam at third harmonic (266 nm), with a moderate repetition rate (50 and 1000 Hz), was used to create regular periodic nanostructures upon polystyrene (PS) thin films. Typical Low Spatial Frequency LIPSSs (LSFLs) were obtained for 50 Hz, as well as for 1 kHz, in cases of one spot zone, and also using a line scanning irradiation. Laser beam fluence, repetition rate, number of pulses (or irradiation time), and scan velocity were optimized to lead to the formation of various periodic nanostructures. It was found that the surface morphology of PS strongly depends on the accumulation of a high number of pulses (103 to 107 pulses) at low energy (1 to 20 µJ/pulse). Additionally, heating the substrate from room temperature up to 97 °C during the laser irradiation modified the ripples' morphology, particularly their amplitude enhancement from 12 nm (RT) to 20 nm. Scanning electron microscopy and atomic force microscopy were used to image the morphological features of the surface structures. Laser-beam scanning at a chosen speed allowed for the generation of well-resolved ripples on the polymer film and homogeneity over a large area.
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A binary blend of poly(isoprene-block-styrene-block-(2-vinylpyridine)) (ISP) triblock terpolymers, having the same chain length but different compositions, was used to achieve an ordered lattice with 4-fold symmetry of rectangular-shaped rods of poly(isoprene) (I) and poly(2-vinylpyridine) (P). In given conditions, the I and P domains were oriented perpendicularly to the substrate, providing an appealing type of templates for nanopatterning. Thin films were prepared by spin coating, exposed to solvent vapor (providing morphological reorganization), and then characterized by atomic force microscopy, transmission electron microscopy, and grazing-incidence small-angle X-ray scattering. Selective I and P identifications were carried out by AFM and TEM on a model ISP, as well as development of a technique of electronic contrast enhancement to better assign the self-assembly structure in GISAXS.
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Solvothermal vapor annealing (STVA) was employed to induce microphase separation in a lamellar forming block copolymer (BCP) thin film containing a readily degradable block. Directed self-assembly of poly(styrene)-block-poly(d,l-lactide) (PS-b-PLA) BCP films using topographically patterned silicon nitride was demonstrated with alignment over macroscopic areas. Interestingly, we observed lamellar patterns aligned parallel as well as perpendicular (perpendicular microdomains to substrate in both cases) to the topography of the graphoepitaxial guiding patterns. PS-b-PLA BCP microphase separated with a high degree of order in an atmosphere of tetrahydrofuran (THF) at an elevated vapor pressure (at approximately 40-60 °C). Grazing incidence small-angle X-ray scattering (GISAXS) measurements of PS-b-PLA films reveal the through-film uniformity of perpendicular microdomains after STVA. Perpendicular lamellar orientation was observed on both hydrophilic and relatively hydrophobic surfaces with a domain spacing (L0) of â¼32.5 nm. The rapid removal of the PLA microdomains is demonstrated using a mild basic solution for the development of a well-defined PS mask template. GISAXS data reveal the through-film uniformity is retained following wet etching. The experimental results in this article demonstrate highly oriented PS-b-PLA microdomains after a short annealing period and facile PLA removal to form porous on-chip etch masks for nanolithography application.
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A series of poly(cyclohexylethylene)-block-poly(ethylene oxide) (CEO) diblock copolymers were synthesized through tandem anionic polymerizations and heterogeneous catalytic hydrogenation. Solvent-annealed CEO diblock films were used to template dense arrays of inorganic oxide nanodots via simple spin coating of an inorganic precursor solution atop the ordered film. The substantial chemical dissimilarity of the two blocks enables (i) selective inclusion of the inorganic precursor within the PEO domain and (ii) the formation of exceptionally small feature sizes due to a relatively large interaction parameter estimated from mean-field analysis of the order-disorder transition temperatures of compositionally symmetric samples. UV/ozone treatment following incorporation produces an ordered arrangement of oxide nanodots and simultaneously removes the block polymer template. Herein, we report the smallest particles (6 ± 1 nm) templated from a selective precursor insertion method to date using a block polymer scaffold.
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Block polymers incorporating highly incompatible segments are termed "high χ" polymers, where χ is the Flory-Huggins interaction parameter. These materials have attracted a great deal of interest because low molar mass versions allow for the formation of microphase-separated domains with very small (<10 nm) feature sizes useful for nanopatterning at these extreme dimensions. Given that well-established photolithographic techniques now face difficult challenges of implementation at scales of 10 nm and below, the drive to further develop high χ block polymers is motivated by trends in the microelectronics industry. This Viewpoint highlights our perspective on this niche of block polymer self-assembly. We first briefly review the relevant recent literature, exploring the various block polymer compositions that have been specifically designed for small feature size patterning. We then overview the now standard method for the benchmarking χ values between different pairs of polymers and the consequences of low N and high χ on the thermodynamic aspects of microphase separation. Finally, we comment on restrictions going forward and offer our perspective on the future of this exciting area of block polymer self-assembly.
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Successive structural transitions in thin films of asymmetric poly(styrene)-block-poly(lactide) (PS-PLA) block copolymer samples upon exposure to tetrahydrofuran (THF) vapors have been monitored using atomic force microscopy (AFM) and both in situ and ex situ grazing incidence small-angle X-ray scattering (GISAXS). A direct link was established between the structure in the swollen state and the morphology formed in the dried state post solvent evaporation. This was related to the high incompatibility between the constituting blocks of the copolymer that thwarted the system from reaching the homogeneous disordered state in the swollen state under the specific conditions utilized in this study. Upon rapid solvent removal, the morphologies formed in the swollen state were trapped due the fast evaporation kinetics. This work provides a better understanding of the mechanisms associated with block copolymer thin film morphology changes induced by solvent vapor annealing.
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The dynamics of phase separation and final morphologies of poly(acrylonitrile-butadiene-styrene) (ABS)-modified epoxy system based on diglycidyl ether of bisphenol A (DGEBA) cured with 4,4'-diaminodiphenylsulfone (DDS) have been monitored in situ throughout the entire curing process by using optical microscopy (OM), differential scanning calorimetry (DSC), rheometry, and small-angle laser light scattering (SALLS). The evolution of phase separation and final morphologies with substructures were explored by OM. The final morphologies of the blend cured at 150 and 165 °C are of phase-inverted type and are quite different from the final morphologies of the same blend cured at 180 °C, in which the final morphologies are cocontinuous. AFM observations of the fully cured sample confirmed the existence of three different phases, the epoxy continuous phase, SAN (styrene/acrylonitrile) continuous phase, and PB droplets at the interface, with a strong tendency to stay at SAN continuous phase. Furthermore, the continuous epoxy phase contains SAN particles and the continuous SAN phase contains epoxy particles. Cure kinetics and rheological results correspond well with the viscoelastic phase separation revealed by OM. The SALLS results display clearly that the phase separation takes place according to nucleation and growth mechanism followed by spinodal decomposition. The development of light scattering patterns during the second stage phase separation follows the Cahn-Hilliard model of spinodal demixing. Furthermore, the evolution of the scattering vector follows a Maxwell-type relaxation equation establishing the viscoelastic behavior of phase separation. The relaxation time of phase separation can be described by the Williams-Landel-Ferry equation for viscoelasticity. As a whole, the dependence of phase separation on cure temperature and the development of final morphologies and the associated mechanisms were explored in detail for the complex epoxy/ABS system.