Monte Carlo Simulations For Adsorption Behavior Of PAA/PEO On The Solid-Liquid Interafce

PAA/PEO comb polymers, which can be look as a homopolymers or polyblockcopolymers uniformly composed of polyacrylicacid (PAA) segments andpolyethylene oxide(PEO) side chains, are widely accepted as superplasticizer in theconcrete and cement industry to improve the fluidity of the cement-based systems.The adsorption of the PAA/PEO on the cement particles can reduce waterconsumption and increase the strength of the cement without the losing of workabilityand strength, or reduce the amount of cement at the same workability and strength ofcement. Compared with other types of superplasticizers, PAA/PEO polymers have ahigh rate of water reduction and good security collapse, et al., witch have become atopic of intense research.The complex molecular architecture of the PAA/PEO comb polymer make itmore challenging to get a definite mechanism of the adsorbing process, because thebackbone length, the PEO side chains length, and the grafting density of these combpolymers all influence the adsorption properties of the polymers on solid surface. It isgenerally difficult to reveal explicitly the microstructure of the adsorbed layers solelyfrom experimental or theoretical approaches. Computer simulation can fill the gapbetween existing theories and experiments. Furthermore, the effect of the chainarchitecture can easily be taken into account by computer simulation.The Monte Carlo method is also known as the stochastic simulation method,statistical experimental methods or random sampling technique is a method ofcalculation based on the random number. Both the measurable and immeasurablephysical quantities can be get by Monte Carlo simulation, what’s more, the systemchanges can be tracked at the molecular level by Monte Carlo simulation. The maingoal of this work in to study the interaction mechanisms and micro-conformations ofPAA/PEO comb polymers adsorbed on particle surface using Monte Carlo methodbasing predecessors’ experience and practice requirement. The main contents of this thesis are as follows:In order to more effectively and rapidly use the Monte Carlo method tosimulation the adsorption behavior of the comb polymer, a new motion algorithm forthree-bond units in comb polymer was proposed. The static and dynamic properties ofcomb polymer were calculated using the new algorithm; and the new algorithm wascompared with the bond fluctuation model proposed by Larson et al. The resultsshown the new motion algorithm was an effective method for the simulation of combpolymer, the simulation efficiency of the comb polymer was obviously improvedmore than one time in three-dimensional lattice model.Monte Carlo simulations were carried out to investigate the adsorption behaviorof PAA/PEO at the solid-liquid interface with the new movement method and theMetropolis algorithm in a cubic lattice with periodic boundary conditions. Theconformations of PAA/PEO with different chain architecture were gat with the aid ofAuto CAD. The influences of chain architecture of PAA/PEO comb polymer on theproperties of mode chain were studied.The simulations results showed that: The simulations results showed that: themolecular size of the adsorbed polymer was larger than those of the correspondingfree chains, the mean-square radius of gyration mainly depended on the length of thebackbone; there was a conformation transformation of the free polymer form swollencoil to rodlike shape at the backbone length LB=12; the whole adsorb chainpresented a mushroom-like conformation, most of the carboxyl groups,75%of thediethyl groups and small part of the epoxy groups were adsorbed directly at the solidsurface when the polymer was adsorbed, most of the epoxy groups stretched into thesolution, providing shielding against the penetration of the solvent to the solid surface;the backbone length and the side chain length had on affection on the adsorptionability of the comb polymer, but the side chain length have a significant impact on thesteric stabilization of the polymer-cement system.In conclusion, the new motion algorithm for three-bond units was effective, andcan be sued as a dynamic Monte Carlo simulation algorithm for the comb polymer.The Monte Carlo simulation for adsorption behavior of PAA/PEO at the interface is useful for the choosing an applicable polymer for applications.