Thermoanalytical behaviour of some coating free films

Differential scanning calorimetry (DSC) was used in the investigation of the behaviour of coating free films. The films were produced from two film-forming polymers which are chemically different but equally used for producing controlled-release dosage forms: Eudragit NE 30 D (synthetically produced polymethacrylate copolymer) and LustreClear product (mixture containing natural and semi-synthetic components: microcrystalline cellulose, hydroxy-ethyl cellulose, carrageenan and polyethylene glycol). During their comparative analysis the characteristic parameters of the DSC curves obtained with dynamic measurement method were used and their changes as a function of storage conditions and storage time were observed. It was found that the thermoanalytical behaviour of the examined methacrylate-based Eudragit NE and cellulose-based LustreClear films was different. The specific enthalpy change of Eudragit NE fresh films was very little, but it increased considerably during storage. The specific enthalpy change of LustreClear films was much greater but its value shows only a slight further increase during storage. The results obtained help to choose the proper temperature for coating and drying.     

Physicochemical testing of free films containing non‐soluble components

Eudragit® L 30D‐55 films containing diclofenac sodium in different concentrations (0%, 1%, and 5%) were studied by conventional physicochemical methods and positron annihilation spectroscopy. Diclofenac sodium was found to change the properties of the film formed significantly. Positron annihilation spectroscopy was applied to track the Eudragit–diclofenac interaction. The presence of diclofenac initially led to significant distortion of the structure of the pure Eudragit film. However, during storage (17°C, 65% relative humidity), the distorted structure relaxed because of water uptake from the air. At the end of the storage period, the free‐volume size was almost the same in all films. Copyright © 2011 John Wiley & Sons, Ltd.     

Initial lamellar thickness dependency of recrystallization behavior of poly(4‐methyl‐1‐pentene)

The isothermal crystallization and subsequent melting process in semicrystalline poly(4‐methyl‐1‐pentene) were investigated via temperature‐dependent small‐ and wide‐angle X‐ray scattering and Flash DSC techniques. In a phase diagram of inversed crystalline lamellar thickness and temperature, the crystallization and melting lines can be described by two linear dependencies of different slopes and different limiting temperatures at infinite lamellar thickness. Upon subsequent heating, recrystallization lines with different slopes were observed for samples with different lamellar thickness, indicating changes in surface free energy difference between stabilized crystallites and mesomorphic phase. The surface free energy of native crystallites with extended‐chain conformation decreased with increasing lamellar thickness due to a more ordered surface region and less chain ends which changes cooperatively with mesomorphic phase. The surface free energy of stabilized crystallites remained unchanged for all lamellar thickness. Therefore, the recrystallization lines with different slopes are consequences of changes in surface free energy of mesomorphic phase. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 219–224     

Reflection–absorption infrared spectroscopy investigation of the crystallization kinetics of poly(ethylene terephthalate) ultrathin films

Reflection–absorption infrared spectroscopy was used to study the crystallization behavior of poly(ethylene terephthalate) (PET) ultrathin films. The crystallinity of ultrathin films was estimated by the fraction of trans conformers of PET. The isothermal and nonisothermal crystallization kinetics of ultrathin films with different thicknesses were investigated. The thinner PET film showed slower kinetics during isothermal crystallization than the thicker film. Moreover, the final crystallinity of films with various thicknesses were reduced with decreasing thickness. An Avrami equation was used to fit the acquired results. The Avrami exponents decreased with the film thickness. As for the nonisothermal crystallization, the cold‐crystallization starting temperature shifted to a lower temperature as the film thickness increased. The influence of the substrate on the crystallization kinetics of the films was also studied. The half‐crystallization times and final crystallinities of ultrathin films adsorbed onto a self‐assembled‐monolayer‐treated surface and an untreated substrate were clearly different, although their thickness dependence was similar. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4440–4447, 2004     

聚3-羟基丁酸酯薄膜结晶的ATR-FTIR研究

使用匀胶机(spincoater),通过溶液铸膜的方法,在铝箔基板上制备出具有不同厚度的聚3羟基丁酸酯(PHB)薄膜.20℃室温条件下,通过衰减全反射傅立叶红外光谱(ATRFTIR)原位观测了不同厚度薄膜的结晶过程,并通过偏光ATRFTIR对薄膜中PHB分子的取向进行了研究.ATRFTIR原位观测结果显示,PHB在薄膜中的结晶速率以及结晶度均随着薄膜厚度的减小而逐渐降低;同时,偏光ATRFTIR测试结果表明,随膜厚减小,薄膜中结晶部分的PHB分子逐渐倾向于沿垂直于基板表面方向取向,膜越薄,倾向越明显.可以认为,PHB分子与基板间的相互作用以及扩散控制结晶导致了上述现象的产生.     

成核剂和促进剂对聚对苯二甲酸乙二酯结晶的影响

研究了一种成核剂和结晶促进剂及其混合物对聚对苯二甲酸乙二酯（ＰＥＴ）结晶过程和熔融行为的影响．结果表明,成核剂的引入降低了ＰＥＴ的结晶成核界面自由能,起到促进ＰＥＴ结晶成核的作用,从而加快了ＰＥＴ的结晶速度．而结晶促进剂对ＰＥＴ的结晶速度影响很小,不能促进ＰＥＴ的成核结晶,但能使ＰＥＴ结晶更完善,使ＰＥＴ的结晶度提高．当两者并用时,ＰＥＴ由熔体降温的结晶行为主要由成核剂控制,而成核促进剂的作用不明显．     

THE EFFECT OF CLAY DISPERSION ON THE CRYSTALLIZATION AND MORPHOLOGY OF POLYPROPYLENE／CLAY COMPOSITES

PP/clay composites with different dispersions, namely, exfoliated dispersion, intercalated dispersion and agglomerates and particle-like dispersion, were prepared by direct melt intercalation or compounding. The effect of clay dispersion on the crystallization and morphology of PP was investigated via PLM, SAXS and DSC. Experimental results show that exfoliated clay layers are much more efficient than intercalated clay and agglomerates of clay in serving as nucleation agent due to the nano-scale dispersion of clay, resulting in a dramatic decrease in crystal size (lamellar thickness and spherulites) and an increase of crystallization temperature and crystallization rate. On the other hand, a decrease of melting temperature and crystallinity was also observed in PP/clay composites with exfoliated dispersion, due to the strong interaction between PP and clay. Compared with exfoliated clay layers, the intercalated clay layers have a less important effect on the crystallization and crystal morphology. No effect is seen for samples with agglomerates and particle-like dispersion, in regard to melting temperature, crystallization temperature, crystal thickness and crystallinity.     

Sintering of Sol-Gel Films

The sintering of films differs from that of bulk gels in several ways. The initial state of a film is generally denser and less crosslinked than a bulk gel made from the same sol, and these factors enhance the densification rate of the film. The substrate constrains the shrinkage of the film, leading to high stresses that retard densification and can influence phase changes. The substrate is a site for heterogeneous nucleation, and crystallization makes densification more difficult, so the competition between sintering and crystallization is particularly important for films. Fast heating favors densification over crystallization, so rapid thermal annealing usually produces denser films. The high surface to volume ratio of a thin film makes it susceptible to degradation by reaction with the substrate and the atmosphere, so choosing compatible materials and avoiding over-firing is essential.     

On sub-T(g) dewetting of nanoconfined liquids and autophobic dewetting of crystallites

The glass transition temperature (T(g)) of thin films is reduced by nanoconfinement, but it is also influenced by the free surface and substrate interface. To gain more insights into their contributions, dewetting behaviors of n-pentane, 3-methylpentane, and toluene films are investigated on various substrates as functions of temperature and film thickness. It is found that monolayers of these molecules exhibit sub-T(g) dewetting on a perfluoro-alkyl modified Ni substrate, which is attributable to the evolution of a 2D liquid. The onset temperature of dewetting increases with film thickness because fluidity evolves via cooperative motion of many molecules; sub-T(g) dewetting is observed for films thinner than 5 monolayers. In contrast, monolayers wet substrates of graphite, silicon, and amorphous solid water until crystallization occurs. The crystallites exhibit autophobic dewetting on the substrate covered with a wetting monolayer. The presence of premelting layers is inferred from the fact that n-pentane crystallites disappear on amorphous solid water via intermixing. Thus, the properties of quasiliquid formed on the crystallite surface differ significantly from those of the 2D liquid formed before crystallization.     

Crystalline morphology evolution in PCL thin films

The transition of crystalline morphology is revealed in poly(?‐caprolactone) (PCL) thin films as the polymer film thickness changes from hundreds of nanometers to several nanometers. The PCL can crystallize into spherulites, dense‐branching morphology (DBM), or dendrites, depending on the polymer film thickness. It was found that when the polymer film thickness approaches 2Rg (radius of gyration of polymer), there is a remarkable change in crystalline morphology. Under this condition, the polymer crystallization is a diffusion‐controlled process. When the value of polymer film thickness closes to Rg, PCL cannot crystallize, and a dewetting phenomenon will take place. Moreover, polymer morphology can be controlled by varying supercooling. The effect of molecular weight on polymer morphology has been investigated. The main factors that affected pattern formation in nonequilibrium crystallization are also discussed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1303–1309, 2005     

Mixed system of Eudragit s-100 with a designed amphipathic peptide: control of interfacial elasticity by solution composition

We report an interfacially active system based on an informational peptide surfactant mixed with an oppositely charged polyelectrolyte. The 21-residue cationic peptide, AM1, has previously been shown to respond reversibly to pH and metal ions at fluid interfaces, forming elastic films that can be rapidly switched to collapse foams or emulsions on demand. Here we report the reversible association of AM1 with the methacrylate-based anionic polymer Eudragit S-100. The strength of the association, in bulk aqueous solution, is modulated by added metal ions and by ionic strength. Addition of zinc ions to the peptide-polymer system promotes complex formation and phase separation, while addition of a chelating agent reverses the association. The addition of salt weakens peptide-polymer interactions in the presence or absence of zinc. At the air-water interface, Eudragit S-100 forms an elastic mixed film with AM1 in the absence of metal, under conditions where the peptide alone does not show interfacial elasticity. When zinc is present, the elasticity of the mixed film is increased, but the rate of interfacial adsorption slows due to formation of peptide-polymer complexes in bulk solution. An understanding of these interactions can be used to identify favorable foam-forming conditions in the mixed system.     

Polymer crystallization of ultrathin films on solid substrates

Recently, polymer crystallization in ultrathin films (thickness less than 100 nm) on solid substrates has attracted increased attention. As it can be considered to be a quasi-two-dimensional (2D) system with one-dimensional (1D) confinement along the substrate normal, ultrathin polymer film offers unique possibilities for testing the theories of crystallization and for studying the effects of confinement and interface which may invoke new mechanisms other than those applied in bulk crystallization of polymers. In this article, we will summarize the important results of ultrathin film crystallization of polymers obtained in the past decades. The morphologies, the crystallization kinetics, and the transformation between monolayer crystals with various metastabilities are reviewed in depth, with an attempt at discussing the ultrathin polymer film crystallization in the general framework of thermodynamics and kinetics of crystallization.     

聚合物纳米粒子乳液的制备及性能研究——添加组分对乳胶粒子形态及胶膜吸水率的影响

本文采用种子微乳液聚合方法,经后期氨化反应,合成了聚丙烯酸酯纳米粒子乳液,讨论了乳化剂、缓冲剂和水溶性丙烯酸单体等添加组分对乳粒子形态和胶膜吸水率的影响,并探讨了微乳液聚合的反应机理。     

Synthesis and characterization of positively charged,alumina‐coated silica/polystyrene hybrid nanoparticles via pickering miniemulsion polymerization

Positively charged, raspberry‐like hybrid nanoparticles, consisting of a polystyrene core and an alumina‐coated silica shell were successfully prepared in a surfactant free system via the radical copolymerization of styrene (St) and different comonomers (acrylic acid, methacrylic acid, and acrylamide) by using a cationic silica sol as the sole emulsifier in Pickering miniemulsion polymerization. The influence of different parameters like pH of the dispersion, comonomer content, and the amount and size of silica nanoparticles on the colloidal stability of the systems, prepared with different comonomers, was examined. The particles' morphology was observed via high‐resolution scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The removal of free silica particles via centrifugation was proved by TEM and SEM, and the content of free and adsorbed silica was quantified via thermogravimetric analysis (TGA). © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Crystallization and melting of isotactic polypropylene crystallized from quiescent melt and stress‐induced localized melt

Temperature dependency of crystalline lamellar thickness during crystallization and subsequent melting in isotactic polypropylene crystallized from both quiescent molten state and stress‐induced localized melt was investigated using small angle X‐ray scattering technique. Both cases yield well‐defined crystallization lines where inverse lamellar thickness is linearly dependent on crystallization temperature with the stretching‐induced crystallization line shifted slightly to smaller thickness direction than the isothermal crystallization one indicating both crystallization processes being mediated a mesomorphic phase. However, crystallites obtained via different routes (quiescent melt or stress‐induced localized melt) show different melting behaviors. The one from isothermal crystallization melted directly without significant changing in lamellar thickness yielding well‐defined melting line whereas stress‐induced crystallites followed a recrystallization line. Such results can be associated with the different extent of stabilization of crystallites obtained through different crystallization routes. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 957–963     

Preparation and characterization of pancreatic lipase immobilized in Eudragit-matrix

Pancreatic lipase (EC 3.1.1.3) was immobilized by entrapping in a commercial preparation of acrylic/methacrylic acid ester-based copolymer (Eudragit E 30 D). The activity of the immobilized lipase beads with a diameter of 1.5-2.0 mm was found to be lower than that of the free lipase. The optimum pH was shifted to the alkaline region and the thermal stability increased, whereas the optimum temperature level remained unchanged. The most important reason for the decreased activity was diffusion limitations. The diffusion of the substrate and products became more pronounced, and lipolytic activity increased upon addition of n-hexane into the reaction medium. The storage and operational stabilities of the immobilized lipase were investigated, and both characteristics were found to be increased when compared to the free enzyme. Furthermore, mechanical or magnetic stirring during the operation were found to have no influence on the carrier-matrix as determined by nephelometric measurements.     

马来酸类可聚合乳化剂及其在乳液聚合中应用

使用可聚合乳化剂可以很好地解决传统乳化剂的缺点,提高乳液的应用性能.马来酸类乳化剂其可聚合基团反应活性适中,可以很好地键合在乳胶粒表面上,且更为突出的是这类乳化剂不易发生均聚,而是倾向于与单体发生共聚.研究表明,马来酸类可聚合乳化剂应用到乳液聚合中,可以改善乳胶液的性能,提高乳胶膜的耐水性等.文章介绍了这一类新型的乳化剂,并根据其亲水基团进行了分类,分别介绍其合成路线,总结了马来酸类乳化剂的特点,概述了在常见乳液聚合体系中的应用与研究.     

A facile method for the preparation of monodisperse hollow silica spheres with controlled shell thickness

This article presents a facile, effective, mild synthesis process for well‐defined hollow spheres by using cationic polystyrene (PS) submicro‐particles as templates. In this approach, the cationic PS templates can be first prepared via emulsifier‐free polymerization by using the cationic monomer 2‐(methacryloyloxy) ethyltrimethylammonium chloride as comonomer, then, the silica shells from the sol‐gel process of tetraethoxysilane were coated on the surfaces of template particles via electrostatic interaction, finally the PS was dissolved in situ by modification of the reaction conditions in the same medium to form monodisperse hollow silica spheres with controlled shell thickness. Fourier transform‐infrared spectroscopy, thermogravimetric analysis, Brunauer‐Emmett‐Teller, transmission electron microscopy, and scanning electron microscope measurements were used to characterize these hollow silica spheres. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1332–1338, 2010     

Molecular simulation of crystallization in n-alkane ultrathin films: effects of film thickness and substrate attraction

Crystallization in n-alkane ultrathin films supported by solid substrates is investigated by molecular dynamics simulation. We consider a relatively short n-alkane, undecane C11H24, on a flat substrate of varied degree of attraction. By the use of the united atom model for n-alkane, we reveal several characteristics of the thin film crystallization. It is found that the crystalline films consist of thin crystalline lamellae where chains are either parallel or perpendicular to the substrate. The relative amount of both types of lamellae changes systematically with film thickness, substrate attraction, and crystallization temperature; thicker films on substrates of higher attraction comprise dominant parallel lamellae, while thinner films on substrates of weaker attraction prefer the perpendicular lamellae. A clue to the morphogenesis is suggested to be the marked preference of the chain ends to locate on the free surface and on the effectively repulsive substrate. It is also shown that the perpendicular crystals, both on the free surface and on the solid substrate, have melting points higher than that of the bulk.     

Colloidal stability of aqueous polymeric dispersions: effect of pH and salt concentration

Aqueous film coatings often contain some electrolytes, organic acids, and pigments to give functions of sustained release, time-controlled release, or protection against light. Additions of some electrolytes or organic acids into latex dispersion for an aqueous film coating affect its colloidal stability. We characterized the aqueous polymeric latexes used in the pharmaceutical industry by measuring zeta potential and particle size, and evaluated this colloidal stability using DLVO theory. Three polymethacrylate-based aqueous polymeric latexes, Eudragit L30D-55, Eudragit RS30D and Eudragit NE30D, having anionic, cationic, and neutral polymer, respectively, were used in this study. The Hamaker constant of the polymethacrylate-based latex was determined to be 6.35 x 10(-21) J, and the total potential energy of the latex dispersion was calculated. The total potential energy of interaction between pairs of latex particles changes by altering the salt concentration and pH. The experimental results of stability in the anionic and the cationic latex dispersions can be explained by the total interaction energies. However, the stabilization of the neutral latex did not match the calculated result. The steric interaction produced by the surfactant likely resulted in the stable dispersion of this latex.