Freezing or wrapping: the role of particle size in the mechanism of nanoparticle-biomembrane interaction

Understanding the interactions between nanoparticles (NPs) and biological matter is a high-priority research area because of the importance of elucidating the physical mechanisms underlying the interactions leading to NP potential toxicity as well as NP viability as therapeutic vectors in nanomedicine. Here, we use two model membrane systems, giant unilamellar vesicles (GUVs) and supported monolayers, to demonstrate the competition between adhesion and elastic energy at the nanobio interface, leading to different mechanisms of NP-membrane interaction relating to NP size. Small NPs (18 nm) cause a "freeze effect" of otherwise fluid phospholipids, significantly decreasing the phospholipid lateral mobility. The release of tension through stress-induced fracture mechanics results in a single microsize hole in the GUVs after interaction. Large particles (>78 nm) promote membrane wrapping, which leads to increased lipid lateral mobility and the eventual collapse of the vesicles. Electrochemical impedance spectroscopy on the supported monolayer model confirms that differently sized NPs interact differently with the phospholipids in close proximity to the electrode during the lipid desorption process. The time scale of these processes is in accordance with the proposed NP/GUV interaction mechanism.     

Evaluation of the role of pores during strength testing in compacts made from different particle size fractions of sucrose

The purpose of this study was to investigate the role of pores in the fracture of circular compacts and to predict compact properties and critical crack lengths. Four different particle size fractions of sucrose, ranging from 20 to 500 microm, were compressed into circular discs (i.e. flat tablets) and rectangular beam specimens of porosity between 30 and 14%. Modelling of the relationship between the tensile strength of the circular discs and the compact porosity indicated extensive fragmentation during compaction for particles in the size range of 250-500 microm, accompanied by a change in densification mechanism for very coarse particles (355-500 microm). When determining the critical stress intensity factor from rectangular single edge notched beam specimens by 3-point bending, an apparent influence of particle size on the values could be seen, whereby here the results indicated that the critical particle size for fragmentation to occur is about 20-40 microm. It was possible to predict the critical stress intensity factor of the compacts from the median pore size and the tensile strength of the circular disc specimens by interpolation of the critical crack length for propagation to occur. The results indicated that for sucrose compacts regardless of their porosity, the pores themselves acted as stress concentrators, not as sharp cracks. For sucrose compacts, crack propagation hence proceeds most likely along grain boundaries.     

The role of particle size on the deposition efficiency of ink on plastic spheres

Experimental investigation of the effect of carbon particle size on its deposition efficiency on the surface of plastic particles has been performed in stirred vessel. A model based on Langmuir kinetics was used, and it provided a good fit for the experimental results. The effect of de-inking conditions such as, carbon particle size, calcium chloride concentration, and carbon concentration has been investigated.

Different sizes of carbon particles were tested. It was found that the deposition rate and the deposition efficiency were generally higher for the larger carbon particles.

The effect of CaCl₂ concentration on the deposition efficiency was investigated. Results showed that the deposition rate increased when the concentration of CaCl₂ increased from 0.05 to 0.10 g/l (the stochiometric ratio needed to react with sodium stearate). Moreover, the deposition efficiency was higher at this concentration. Concentrations above the stochiometric ratio did not show a systematic behavior for the deposition rate and the deposition efficiency.

Finally, the effect of carbon concentration was examined. Carbon concentration of 0.25, 0.30, and 0.40 g/l were used. Results showed that the concentration of carbon did not affect the deposition efficiency nor the rate of deposition.

This study confirmed the applicability of the method of ink removal from recycled waste paper using plastic particles, proposed by previous investigators.     

The role of surfactant in controlling particle size and stability in the miniemulsion polymerization of polymeric nanocapsules

The influence of surfactant concentration on particle size and stability of nanocapsules with liquid cores, synthesized by an in situ miniemulsion polymerization process, was investigated. Although the role of surfactant in the synthesis of particles in the nanometer range has frequently been documented, the transition to structured particles, which almost consist of a 1:1 weight ratio of encapsulated liquid hydrophobe to polymeric shell, has not received much attention. Capillary hydrodynamic fractionation (CHDF) analyses were used to evaluate particle size. Results were subsequently used to stoichiometrically calculate the area which is occupied per surfactant molecule on the particle surface. These results were compared with “classical” miniemulsion data, i.e. data generated from the synthesis of polymeric latexes in the presence of a hydrophobe, but at a much lower hydrophobe:monomer ratio as was used here. The surface coverage per surfactant molecule could be related to the surface tension of the latex, thus providing a relationship between particle size and stability. CHDF was furthermore used to investigate particle size after grafting of a secondary PMMA shell. Data obtained from CHDF experiments were in all cases confirmed by TEM analysis of the synthesized particles. To conclude, the synthesis of nanocapsules with liquid cores could be successfully scaled-up, with retention of all the characteristics of the final latex.     

Analysis of particle size distribution in colloidal dispersions by electron microscopy

Summary Particle size distribution data have been determined by electron microscopy for dispersions containing known mixtures of monodisperse polystyrene latices of diameters in the range 0.08–0.4μ, and particle concentrations of 10⁶–10⁸ particles ml⁻¹, and good agreement was found for grid specimens prepared by centrifugation.     

An expeditious method for determining particle size distribution by near infrared spectroscopy: Comparison of PLS2 and ANN models

The particle size distribution of a solid product can be crucial parameter considering its application to different kinds of processes. The influence of particle size on near infrared (NIR) spectra has been used to develop effective alternative methods to traditional ones in order to determine this parameter. In this work, we used the chemometrical techniques partial least squares 2 (PLS2) and artificial neural networks (ANNs) to simultaneously predict several variables to the rapid construction of particle size distribution curves. The PLS2 algorithm relies on linear relations between variables, while the ANN technique can model non-linear systems.Samples were passed through sieves of different sieve opening in order to separate several size fractions that were used to construct two types of particle size distribution curves. The samples were recorded by NIR and their spectra were used with PLS2 and ANN to develop two calibration models for each. The correlation coefficients and relative standard errors of prediction (RSEP) have been used to assess the goodness of fit and accuracy of the results.The four calibration models studied provided statistically identical results based on RSEP values. Therefore, the combined use of NIR spectroscopy and PLS2 or ANN calibration models allows determining the particle size distributions accurately. The results obtained by ANN or PLS2 are statistically similar.     

Determination of crystallite particle size distribution of polymers from WAXS

A method for the calculation of crystallite size distributions from the profile of wide-angle x-ray reflections is developed. The influence of lattice distortions on the profile is taken into account. The information about the lattice distortions is obtained from the measurement of the integral widths of a number of reflections. The method is applied to samples of (ethylen-1 hexen) copolymers. The change of crystallite size distributions in lateral directions with increasing temperature (20–121°C) is measured. Recrystallization processes at temperatures near the melting point are observed. © 1996 John Wiley & Sons, Inc.     

Role of emulsifier on the particle size and polymer particle size distribution using multiwavelength spectroscopy measurements

Latex emulsions depend strongly on the polymer composition, and particle size distribution, which in turn, is a function of the preparation of the latex and on the formulation and composition variables. This study reports measurements of particle size and particle size distribution of latex emulsions as function of the reaction time and the type and concentration of emulsifier by using the multiwavelength spectroscopy technique. Results show changes in the particle size of latex emulsions with the reaction time, obtaining larger particles and broader distributions with increasing of Tween 80 ratio. The steric stabilization provides the sole nonionic emulsifier is not enough to protect the polymer particle, causing the flocculation among the interactive particles, resulting in unstable latex. However, latex emulsions prepared with Tween 80 ratio <70 wt.% can stabilize efficiently the nucleated particles, probably due to the effects provided by both, the electrostatic and steric stabilization mechanisms. The same effect is shown in the curves of conversion (%) as a function of reaction time, resulting in slower polymerization rate for Tween 80 ratio >70 wt.%. On the other hand, smaller polymer particles, in all range of emulsifier mixture, have been obtained to higher emulsifier concentration.     

Emulsion polymerization: On the characterization of the particle size distribution

In emulsion polymerization, the polymer particles generated exhibit a size distribution. Broadness of the distribution is usually characterized by the uniformity (D_p), a ratio of weight to number average particle sizes, and is found to decrease with reaction time despite the fact that the particle volume distribution is usually broadened. Based on the mathematical model proposed by Lichti, Gilbert, and Napper, detailed analysis using the method of moment shows that standard deviation of the particle volume distribution increases with time, while that of the particle diameter distribution decreases with time. D_p's of both volume and diameter distributions all show decreasing with reaction time. These results are in agreement with those found experimentally. The present analysis indicates that, in the characterization of the broadness of the PSD in the emulsion polymerization, one has to be aware of the difference in meanings among these parameters related to the broadness of the PSD.     

Dispersion polymerization of methyl methacrylate in supercritical carbon dioxide: Influence of helium concentration on particle size and particle size distribution

Dispersion polymerizations of methyl methacrylate utilizing poly(1,1,-dihydroperfluorooctyl acrylate) as a steric stabilizer in supercritical carbon dioxide (CO₂) were carried out in the presence of helium. Particle size and particle size distribution were found to be dependent on the amount of inert helium present. Particle sizes ranging from 1.64 to 2.66 μm were obtained with various amounts of helium. Solvatochromic investigations using 9-(α-perfluoroheptyl-β,β-dicyanovinyl)julolidine indicated that the solvent strength of CO₂ decreases with increasing helium concentration. This effect was confirmed by calculations of Hildebrand solubility parameters. Dispersion polymerization results indicate that PMMA particle size can be attenuated by the amount of helium present in supercritical CO₂. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2009–2013, 1997     

Nanoparticle precipitation in reverse microemulsions: particle formation dynamics and tailoring of particle size distributions

In this work, a detailed experimental analysis of the nanoparticle formation dynamics and the formation mechanism in a reverse microemulsion system is given. The precipitation of barium sulfate nanoparticles inside microemulsion droplets is investigated at the molecular scale with respect to the evolution of the particle size distribution and the particle morphology by an extensive transmission electron microscope (TEM) analysis. Different mixing procedures (feeding strategies) of two reactants, barium chloride and potassium sulfate, are evaluated concerning their ability for a tailored particle design under consideration of the complete particle size distribution (modality and polydispersity). It is shown that improved knowledge about the particle formation mechanisms, the dynamics, and the influence of the colloidal microemulsion structure could be used for a tailored design of particles,for example, controlled synthesis of nanoparticles with a bimodal particle size distribution by the application of a sophisticated feeding strategy.     

Miniemulsion polymerization of styrene: Evolution of the particle size distribution

The mechanism of the miniemulsion polymerization of styrene was investiaged through a combination of calorimetry to monitor the polymerization rate and transmission electron microscopy (TEM) to follow the evolution of the particle size distribution. These techniques proved to be a powerful combination for gaining detailed mechanistic information regarding these polymerizations. Particle size analysis of the latexes withdrawn during the course of the reaction revealed that most of the polymer particles were formed by a relatively low conversion (i.e., 10% conversion). However, nucleation continued well past this point (to 40-60% conversion). In fact, it was observed that nucleation in miniemulsion polymerizations using cetyl alcohol continued past the maximum in the rate of polymerization. As a result of these long nucleation periods, the latex particle size distributions produced from these miniemulsion polymerizations were broader than their conventional emulsion polymerization counterparts, and were negatively skewed with a tail of small particles. The amount of negative skewing of the particle size distributions was found to decrease with increasing initiator (potassium persulfate) concentration. Finally, a correlation was observed between the length of time to the maximum polymerization rate and the breadth of the particle size distribution as reflected in the standard deviation. © 1995 John Wiley & Sons, Inc.     

渣油中沥青质分子颗粒尺寸及其胶粒模型研究

分别以苯和硝基苯为溶剂测定了大庆、胜利、孤岛和辽河减压渣油沥青质、胶质和芳香分的分子量；依据球形分子模型计算了这些物质的分子尺寸；构筑了渣油中沥青质胶粒（胶团）模型，并依此计算了渣油中沥青质胶粒尺寸。结果表明，以硝基苯为溶剂所测沥青质分子量更能反应沥青质化学结构的实质；就原始沥青质来说，以苯为溶剂测得的沥青质分子直径为3.8 nm～5.0 nm,以氯代苯为溶剂测得的分子直径为3.2 nm～3.7 nm,以硝基苯为溶剂测得的分子直径为2.8 nm～3.2 nm；辽河、胜利与大庆减压渣油中沥青质的胶粒直径为10.0 nm～11.0 nm，孤岛减压渣油中沥青质的胶粒直径为9.0 nm～10.0 nm。     

Nanospheres in a nematic liquid crystal solvent: the influence of particle size

We use Monte Carlo simulations to investigate a simple lattice model for nematic liquid crystals containing nanospheres. The influence of particle size on the phase behaviour is studied using two different sized particles. The phase diagram is found to be topologically equivalent for both particle sizes, with a large biphasic region corresponding to coexistence between a rod-rich nematic and a rod-poor isotropic phase. For small spheres, the rod-rich nematic phase is stable for relatively large volume fractions of spheres (up to a maximum of about 16%). In contrast, the nematic phase for the system with larger spheres is constrained to a much narrower region of the phase diagram.     

Examination of the role of ion size in determining double layer properties on the basis of a generalized mean spherical approximation

A new model for the diffuse double layer which accounts for the effects of ion size and solution permittivity is described. It is then used to estimate the potential drop across the diffuse layer at negative charge densities for the cases that Li⁺ and Cs⁺ are the electrolyte cations. The potential drop in the Li⁺ system is considerably smaller than that in the Cs⁺ system at 1 M, and both values are smaller than the value predicted by the Gouy–Chapman model. As the electrolyte concentration decreases these differences become smaller so that at 0.01 M, the present model predicts that the diffuse layer potential drop is approximately 90% of the Gouy–Chapman estimate. The results of the model are used to examine the differences in inner layer structure at mercury electrodes with Li⁺ and Cs⁺ ions at the outer Helmholtz plane, and to reconsider the question of the specific adsorption of Cs⁺ at negative-charge densities.     

Emulsion polymerization: Theory of particle size distribution in copolymerization system

A mathematical model for describing the particle size distribution (PSD) in emulsion copolymerization system is developed by analogy to that in emulsion homopolymerization system as proposed by Lichti and co-workers. By use of the appropriate combinations of the kinetic parameters of the comonomers, the complicated equations for copolymerization systems can be reduced to simpler equations identical to those of homopolymerization systems. The two calculation examples, styrene–methyl methacrylate and styrene-butadiene systems, are given to demonstrate the applicability of the proposed theory. The conditions for producing bimodal PSD from a seeded emulsion polymerization are discussed.     

Molecular mobility in rubbery composites: Effect of filler particle size

We have measured proton NMR T₂ relaxation spectra in Arco R45M OH-terminated poly-butadienes (PBs) cured with isophorone diisocyanate and filled with 65 wt % SiO₂ particles of each of six different average sizes. Identifying the short T₂ component with the gel, we find that the gel fraction is displaced from nominal NCO/OH stoichiometry, probably as a result of water adsorbed on filler particle surfaces. Near effective stoichiometry and in the presence of filler, molecular and segmental mobilities decrease, most strongly in specimens with the smallest filler particles. Comparison with parallel Monte Carlo simulations of the PB matrix geometry indicates that segmental mobility and sol migration decrease uniformly in a wide vicinity of the filler particles. Thus the rigidification of the matrix measured via NMR has a range of approximately 1-3 μm from nearby filler particle surfaces, representing the rms diffusion distance of the light components of the sol during the T₂ relaxation. © 1993 John Wiley & Sons, Inc.     

On the evolution of particle size average and size distribution in suspension polymerization processes

The dispersion of methyl methacrylate (MMA) and its suspension polymerization were used as models to elaborate the evolution of particle size average and size distribution in the course of suspension polymerization. The underlying mechanisms for the occurrence of the dynamic and static steady states in the population of drops were defined and their effects on the evolution of drop/particle size average and size distributions were examined. The characteristic intervals of suspension polymerizations (transition, steady-state, growth, and identification) were elaborated. The formation of satellite droplets and their evolution in the course of polymerization were also discussed.     

Tailoring the particle size of monodispersed colloidal gold

Monodispersed spherical gold particles ranging in modal diameter from 80 nm to 5 μm, were prepared by reducing tetrachloroauric(III) acid with iso-ascorbic acid in aqueous solutions at 20°C. The particle size was altered by changing the pH, which affected the composition of gold(III) solute complexes. The latter controlled the redox potential of the system, essential to the formation of the initial nanosize gold dispersions. Depending on the experimental conditions, the resulting primary particles remained either stable or they aggregated to form much larger uniform spheres. The mechanisms of the precipitation of the precursors (primary) particles and of their mutual interactions to yield the final dispersions are discussed.