Does morphology stick? Tailored particle morphologies by swelling polymerization process

Structured dispersion particles suitable for pressure sensitive adhesives (PSA) were synthesized via swelling polymerization technique (EP 359562). Particles consisting of poly(n‐butyl acrylate) copolymerized with different types of carboxylic acids were used as seeds. The final particles were synthesized by swelling polymerization process, using 6 wt % styrene or 6 wt % methyl methacylate. The resulting particle morphology was analyzed by atomic force microscopy (AFM) and transmission electron microscopy (TEM). From previous works (Coll Surf A 2001, 183–185, 725–737; J Appl Polym Sci 2004, 91, 2610–2623) where two‐step emulsion polymerization was used on similar particles, it is expected that the particle morphology is affected by the polarity of the monomer used for swelling polymerization because of the phase compatibility (thermodynamic parameter). In this work, the seed particles used were always of a glass transition temperature (T_g) below polymerization temperature. The diffusion of the growing polymer chains from the swelling polymerization is therefore mainly affected by their own T_g and the influence of the carboxy groups on the chain length of the entering radicals (kinetic parameter). The different morphologies of the single particles are discussed qualitatively. The effects of reaction parameters are compared with the results given in the previous work. The structure of the corresponding dispersion films was characterized using AFM. Correlations to macroscopic properties such as the cohesive strength and peel adhesion to different substrates are discussed. The results are also compared with the application properties of the corresponding unmodified particles, statistical copolymers, and to blends with small sized PMMA or PS particles. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1444–1455, 2006     

纳米PVC树脂有机/无机相结构组装特征及其形成机理研究

用TEM和AFM研究了纳米CaCO3与VCM的原位聚合，发现无机纳米相与PVC有机相结构的组装具有三大典型特征；核壳型，崩解型及微胶囊型，分析了核壳型结构是聚合反应之前纳米颗粒作为无机分散剂吸附在VCM液滴表面形成的：崩解型是VCM单体进入纳米颗粒孔道，发生聚合反应后热量积聚造成的；而微胶囊结构则是纳米颗粒表面在冷分散阶段浓集了引发剂，升温聚合时，纳米颗粒作为提供游离基的刚性骨架，产生了诸多毛杆高分子后形成的结果。     

Immobilization of biologically active species on PA‐6 foils treated by a dielectric barrier discharge

In the field of biomaterials and biomedical devices, surface activation has been focused on creating functional groups capable of preferential adsorption of biologically active species (proteins, enzymes, cells, drugs, etc.). In this way an interface can be created between the synthetic material and the biological medium, with the aim of increasing the compatibility of the implant with the human organism. In our experiments a dielectric barrier discharge (DBD), in helium at atmospheric pressure, was used as the source of energy capable of creating active centers that render the functionalized surface favorable to immobilization of biological molecules. Retention of immunoglobulin (IgG) and heparin biomolecules on polyamide‐6 (PA‐6) surfaces after treatment by the DBD was analyzed by atomic force microscopy, adhesion evaluation, and measurement of the contact angle titration in order to assess this incorporation on the treated surfaces. The marked adsorption of the biomolecules on the active sites created by DBD on the exposed surfaces also was related to a complex set of processes, such as enhanced roughness, increased surface wettability, and modified distribution of cationic and anionic groups on the treated surfaces. All these factors could promote interfacial interactions between the specific groups of the biomolecules existing in the biological medium and the type of cationic and/or anionic groups present on the surface. The efficiency of the DBD treatment showed that the DBD technique is useful for preactivation of the polymer surface for immobilization of other biologically active species (such as drugs and enzymes). © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1985–1990, 2003     

The role of plasticizer on the exfoliation and dispersion and fracture behavior of clay particles in PVC matrix: a comprehensive morphological study

The clay nanoparticles are readily dispersed and exfoliated in the PVC matrix with the help of Dioctyl phthalate (DOP) plasticizer. X-ray, TEM and AFM analysis of the nanocomposites indicate that there is an optimum concentration of DOP for the process. If used in high concentrations, the ability to transfer forces to the clay particles through the polymer matrix decreases due to substantial decrease in viscosity. The individual platy montmorillonite particles dispersed in PVC matrix were directly observed by AFM and found to lie preferentially on their basal surfaces, especially when the compounded batch is compression molded. The edges of the particles were in some cases straight forming hexagonal angles and in other cases irregular.     

Effect of crystallization on morphology-conductivity relationship in polypyrrole/poly(?-caprolactone) blends

Electrically conducting blends, based on polypyrrole (PPy) as the conductive polymer and poly(?-caprolactone) (PCL) as an insulating polymeric matrix, were prepared by polymerizing pyrrole (Py) in its vapor state inside the PCL matrix. The roles of specific interactions between blend components as well as the crystallization of PCL matrix in the resulting morphology have been analyzed by Fourier-transform infrared spectroscopy (FTIR), thermo-optical analysis (TOA) and atomic force microscopy (AFM). The results indicate that PPy is located within both the intra and interspherulitic regions of the PCL matrix achieving a well-developed connected network. Compared with amorphous matrices, considerable conductivity (around 1 S/cm) was raised with the crystalline PCL matrix with only a relatively low level of the conductive polymer (∼5%) in the blend.     

Graft polymerization of vinyl acetate onto silica

The free‐radical graft polymerization of vinyl acetate onto nonporous silica particles was studied experimentally. The grafting procedure consisted of surface activation with vinyltrimethoxysilane, followed by free‐radical graft polymerization of vinyl acetate in ethyl acetate with 2,2′‐azobis(2,4‐dimethylpentanenitrile) initiator. Initial monomer concentration was varied from 10 to 40% by volume and the reaction was spanned from 50 to 70°C. The resulting grafted polymer, which was stable over a wide range of pH levels, consisted of polymer chains that are terminally and covalently bonded to the silica substrate. The experimental polymerization rate order, with respect to monomer concentration, ranged from 1.61 to 2.00, consistent with the kinetic order for the high polymerization regime. The corresponding rate order for polymer grafting varied from 1.24 to 1.43. The polymer graft yield increased with both initial monomer concentration and reaction temperature, and the polymer‐grafted surface became more hydrophobic with increasing polymer graft yield. The present study suggests that a denser grafted polymer phase of shorter chains was created upon increasing temperature. On the other hand, both polymer chain length and polymer graft density increased with initial monomer concentration. Atomic force microscopy–determined topology of the polymer‐grafted surface revealed a distribution of surface clusters and surface elevations consistent with the expected broad molecular‐weight distribution for free‐radical polymerization. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 300–310, 2003     

Direct analysis of annealing of nodular crystals in isotactic polypropylene by atomic force microscopy, and its correlation with calorimetric data

The process of isothermal annealing of nodular monoclinic crystals of isotactic polypropylene (iPP) was analyzed by atomic force microscopy (AFM) and temperature-modulated differential scanning calorimetry (TMDSC). Initially nodular and mesomorphic domains were obtained by controlled melt-crystallization at high cooling rate. Subsequent heating triggers transition from mesomorphic to monoclinic structure, and melting of unstable nodules. Annealing allows re-crystallization, which is recognized by enlargement of domains from initially about 20 nm to about 35 and 55 nm after annealing at 393 and 433 K, respectively. Furthermore, the re-crystallization process is connected with a slight change of the aspect ratio of crystals. The isothermal re-crystallization of the liquid is superimposed by aggregation of crystals, to yield blocky, and string-like objects. The direct analysis of structure on isothermal annealing by AFM is for the first time compared with the isothermal decrease of the apparent specific heat capacity, or change of enthalpy, monitored by TMDSC. The apparent specific heat capacity decreases during annealing with an identical non-linear time dependence as the directly observed growth of the crystal size. Analysis of the annealing processes at different temperatures yields proportionality between the increase of the crystal size and the reduction of the apparent specific heat capacity.     

Segregation in granular materials and the direct measurement of surface forces using atomic force microscopy

It is known that one of the dominant forces controlling the macroscopic motion of particles is the cohesive force due to the presence of liquid bridges between particles. In a mixing process, this force directly impacts the degree of homogeneity achievable by the system. The work presented here provides a quantitative analysis of this relationship through concurrent direct measurements of surface forces due to moisture and blending/segregation experiments. Atomic force microscopy (AFM) was employed to measure the force required to remove the AFM's cantilever from the surface of a glass bead with varying degrees of surface moisture. Corresponding blending/segregation experiments were performed using the same materials and conditions to develop a correlation between the interparticle forces due to the liquid layer and the final state of a mixing process. The extent to which greater moisture content increased the interparticle surface forces was quantified, and it was observed that segregation decreases proportionately to increases in surface forces.     

Al2O3 coated glass by aerosol deposition with excellent mechanical properties for mobile electronic displays

Al₂O₃ thin film was deposited on Gorilla glass using an aerosol deposition method to improve the mechanical property of cover glass for mobile electronic device. The deposited Al₂O₃ film (approximately 1 μm thick) was a polycrystalline structure and showed a high light transmittance of approximately 90% in the visible light region. The CIE color space (L*a*b) measurement also showed a characteristic corresponding to the acceptable optical range of the cover glass. Further, it was confirmed that the bending strength improved by 10 %, as compared with bare Gorilla glass (from 6970 kgf/cm² to 7704 kgf/cm²), and the Vickers hardness increased to approximately 1700–2000 HV, as compared with that of Gorilla glass (<700 HV). Owing to the improved mechanical properties, the Al₂O₃ thin film exhibited good anti-scratch properties and is expected to be applied to the cover glass of various display products.     

闪锌矿BxAl1-xAs合金的LP-MOCVD生长研究

利用低压金属有机化学气相沉积(LP-MOCVD)生长工艺,采用三乙基硼(TEB)源,在GaAs(001)衬底上生长了B并入比为0.4%～4.4%的一系列BxAl1-xAs合金。实验结果表明,BxAl1-xAs的最优生长温度为580℃;当生长温度为550℃和610℃时,BxAl1-xAs中B并入比都会下降,550℃时B并入比下降更为显著。在580℃最优生长温度下,B并入比随着TEB摩尔流量增加而提高,且B并入比从临界值2.1%增加至最大值4.4%时,DCXRDω-2θ扫描BxAl1-xAs衍射峰的半高宽值从51.8 arcsec升高到204.7 arcsec,原子力显微镜(AFM)测试表面粗糙度从2.469 nm增大到29.086 nm,说明B并入比超过临界值后BxAl1-xAs晶体质量已经逐渐严重恶化。