Coupling effect of Brownian motion and laminar shear flow on colloid coagulation:a Brownian dynamics simulation study

Simultaneous orthokinetic and perikinetic coagulations（SOPCs） are studied for small and large Peclet numbers（P e） using Brownian dynamics simulation.The results demonstrate that the contributions of the Brownian motion and the shear flow to the overall coagulation rate are basically not additive.At the early stages of coagulation with small Peclet numbers,the ratio of overall coagulation rate to the rate of pure perikinetic coagulation is proportional to P 1/2 e,while with high Peclet numbers,the ratio of overall coagulation rate to the rate of pure orthokinetic coagulation is proportional to P 1/2 e.Moreover,our results show that the aggregation rate generally changes with time for the SOPC,which is different from that for pure perikinetic and pure orthokinetic coagulations.By comparing the SOPC with pure perikinetic and pure orthokinetic coagulations,we show that the redistribution of particles due to Brownian motion can play a very important role in the SOPC.In addition,the effects of redistribution in the directions perpendicular and parallel to the shear flow direction are different.This perspective explains the behavior of coagulation due to the joint effects of the Brownian motion（perikinetic） and the fluid motion（orthokinetic）.

Effect of local environment in resonant domains of polydisperse plasmonic nanoparticle aggregates on optodynamic processes in pulsed laser fields

Interactions of pulsed laser radiation with resonance domains of multiparticle colloidal aggregates having an increasingly complex local environment are studied via an optodynamic model. The model is applied to the simplest configurations, such as single particles, dimers, and trimers consisting of mono- and polydisperse Ag nanoparticles. We analyze how the local environment and the associated local feld enhancement by surrounding particles affect the optodynamic processes in domains, including their photomodification and optical properties.

Restructuring of plasmonic nanoparticle aggregates with arbitrary particle size distribution in pulsed laser fields

We have studied processes of interaction of pulsed laser radiation with resonant groups of plasmonic nanoparticles（resonant domains） in large colloidal nanoparticle aggregates having different interparticle gaps and particle size distributions.These processes are responsible for the origin of nonlinear optical effects and photochromic reactions in multiparticle aggregates.To describe photo-induced transformations in resonant domains and alterations in their absorption spectra remaining after the pulse action,we introduce the factor of spectral photomodification.Based on calculation of changes in thermodynamic,mechanical,and optical characteristics of the domains,the histograms of the spectrum photomodification factor have been obtained for various interparticle gaps,an average particle size,and the degree of polydispersity.Variations in spectra have been analyzed depending on the intensity of laser radiation and various combinations of size characteristics of domains.The obtained results can be used to predict manifestation of photochromic effects in composite materials containing different plasmonic nanoparticle aggregates in pulsed laser fields.

Two examples of using physical mechanics approach to evaluate colloidal stability

Since Mr.Tsien brought up his idea of physical mechanics,as a new field in engineering science,to public attention in the early 50's of the 20th century,innumerable application examples of physical mechanics approach in diverse fields have manifested its strong vitality increasingly.One of important aspects in applications of physical mechanics is to appropriately choose the microscopic quantity for the system in consideration and build a bridge to connect its relevant microscopic information to its desired macroscopic properties.We present two unique cases of using the physical mechanics approach to study colloidal stability.In the first case we measured the outcomes from artificially induced collisions at individual particle levels,by means of directly observing artificially induced collisions with the aid of optical tweezers.In the second case,by using T-matrix method,the microscopic quantity extinction cross section of the doublet can be accurately evaluated and therefore the measurement range and accuracy of the turbidity methodology for determining the CRC are greatly improved.

Prediction of aggregation behavior of submicron-sized particles of praseodymium-doped zirconium silicate in aqueous suspension by population balance model

The aggregation behavior of submicron-sized particles of praseodymium-doped zirconium silicate, a ceramic pigment, in aqueous suspension was predicted by a modified population balance model, In the model, the collision frequencies were selected to describe evolution of the particle size distribution of the suspension. The collision efficiency was estimated as a function of interaction potential between particles based on Derjaguin-Landau-Verwey-Overbeek theory. The population balance model was modified to predict the stable state of the aggregation by introducing the volume mean size of aggregate to stability ratio. In addition, aggregation of the particles in aqueous suspension in the presence of sodium dodecyl benzene sulfonate or potassium chloride was experimentally investigated. The predicted data （i.e., the final aggregate size, aggregation rate, and particle size distribution） were similar to the experimentalresults.