Soft Polymer Particles Research Articles

Revealing the Aggregation Mechanism, Structure, and Internal Dynamics of Poly(vinyl alcohol) Microgel Prepared through Liquid–Liquid Phase Separation

The use of technologies based on soft polymer particles represents an effective way to deliver target molecules with a specific function. To design a well-performing delivery system, it is fundamental to rationalize both the aggregation and the structural properties of such particles. In this study, we present the kinetic and structural characterization over time of poly(vinyl alcohol) (PVA) microgels obtained through a salting-out process in the presence of NaCl. We have analyzed how both the polymer and salt concentrations affect the aggregation process. The aggregation rate as well as the morphology and physico-chemical parameters, such as mass and chain density of the microgels, have been determined through static and dynamic light scattering and discussed in the framework of the diffusion-limited and reaction-limited colloid aggregation. Insights into the polymer chain arrangements and their dynamics have been gained by means of small-angle neutron scattering and neutron spin-echo measurements. As a ...

Interactions between circulating nanoengineered polymer particles and extracellular matrix components in vitro.

The extracellular matrix (ECM) that surrounds cells in vivo represents a biological barrier for nanomaterials in biomedicine. Herein, we present a system for investigating the interactions between circulating polymer particles and ECM components in vitro using a commercially available flow-based device. We use this system to show how material-dependent interactions of two different particle types-one assembled using poly(ethylene glycol) (PEG) and one prepared using poly(methacrylic acid) (PMA)-affect their interactions with basement membrane extracts during in vitro circulation, with PEG particles remaining in circulation longer than PMA particles. Further, by comparing macroporous hyaluronic acid gel constructs (typically used for tissue engineering) with basement membrane extracts, we show that scaffold-effects (porosity and surface chemistry) impact on circulation time in vitro. The presented system is simple and modular, and can be used to rapidly screen fundamental interactions of engineered particles with biologically relevant microenvironments under flow-conditions.

Effects of the Nanomechanical Properties of Polymer Nanoparticles on Crack Patterns during Drying of Colloidal Suspensions

Coalescence during drying of suspensions containing glassy polymer nanoparticles generates fascinating crack patterns, whereas coalescence of soft polymer particles gives crack-free films. This process is widely used in environmental-friendly water-based coatings, which use nanosized polymer nanoparticles in the film formation process. Numerous studies have shown that polymer nanoconfinement could lead to a drastic modification of the polymer properties such as a reduction of the glass transition temperature (Tg). If such a change in the properties of polymers also exists when nanoconfined in nanoparticles in suspension, then one would expect an alteration in the film formation process, particularly a reduction in the minimum film formation temperature. In this paper we look at the effect of nanomechanical properties of polymer nanoparticles on crack patterns generated by particle coalescence. We study crack pattern morphology during drying of aqueous suspensions of PBMA nanoparticles (50 nm diameter) with different nanomechanical properties (different cross-linking ratios). We investigate the effect of temperature and relaxation time on crack morphologies in the transition from crack to crack-free films. These results were analyzed in terms of time−temperature superposition and compared to bulk behavior.

Formation of microheterogeneous film from composite polymer emulsion prepared by the stepwise heterocoagulation method

Blend emulsion of 2 kinds of particles, in which composite polymer particles were prepared by utilizing the stepwise heterocoagulation method proposed by the authors in 1990, was cast to prepare a microheterogeneous film. In the film, a discontinuous phase consisted of large anionic hard polymer particles and a continuous one consisted of small cationic soft polymer particles with the content of 30 wt % as film-forming additives. The storage stabilities of the blend emulsions after the stepwise heterocoagulation were examined under various conditions. The morphology of the film prepared was estimated from attenuated total reflectance Fourier transform infrared spectroscopic and dynamic mechanical spectroscopic measurements. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2221–2228, 1998

Composite mechanism of polymer modified cement

Microstructure and composite mechanism of polymer modified cement (PMC) and mortar have been studied. Microstructure of PMC was observed by cryo-SEM. Dispersed polymer particles were observed in the hardened body. Polymer films were observed on the surface of hardened samples and at the interface of cement or aggregate in PMC. The bending strength of PMC was increased by the action of soft polymer particles in the hardened body. Adhesive strength of PMC was improved by the formation of polymer films. Both the particle dispersion of polymer and the formation of polymer films are useful as the composite mechanism of PMC.

New Profile of Ultra Low Stress Resin Encapsulants for Large Chip Semiconductor Devices

lnternal stress, as a result of temperature cycle testing (TCT), causes package cracking, passivation film cracking, aluminum pattern deformation, etc. This is particularly evident in IC's and LSI devices with large-size chips and larger memory capacity. Greater reduction of internal stress imparted by resin encapsulants is required to address these problems. To reduce the internal stress, it was previously determined that it is effective to introduce very small sized silicone domains into the epoxy matrix and to create a strong interaction layer between the domain/matrix interface in a heterogeneous structure where soft polymer particles are dispersed as domains in the epoxy matrix as a continuous phase. To date, research efforts have yielded epoxy resins having about 0.1-µm domains with a strong interaction layer at the domain/matrix interface using special silicone modifiers. Comparisons were. made between silicone-modified epoxy resins having 2-5-µm domains and smooth domain/matrix interfaces with versions having 0.1'µm domains. From these comparisons we have drawn the following conclusion: as the silicone domain size decreases within the epoxy matrix, the internal stress imparted by the encapsulant decreases as measured by temperature cycle testing.