Mechanism Studies On Formation Of Polymer Brush On Metal Surface

Polymer brush is a layer of polymers attached with one end to a surface either throughphysical adsorption or chemical bond. The polymer brushes exist in everyday life, much ofthe application polymer brushes originated from their different properties, wetting, corrosion,colloidal stabilization, smart surfaces and biological sensors. In the surfaces with controllablepatterns on a nanometer scale, diblock copolymer brushes have wide application prospects.Compared to experiments and theories, computer simulations can provide a directvisualization on the physical process, and further help us understanding the essence ofphenomena with adsorbing process. Therefore, the investigations of diblock copolymeradsorbed on metal crystal surface have important scientific interest and practical value.In the present work, the case of the surface with different metal crystal attached variousdiblock copolymer (including neutral diblock copolymer, charged diblock copolymer, anddiblock copolymers with various stiffness and temperature) are studied based on molecularsimulation methods, as well as the conformation of polyampholyte chains grafted on thespherical particle is discussed. Additionally, deep investigations into polyampholytes graftedonto spherical particle for interaction between colloids, preventing macromolecules andparticles adsorbing on the surface are of great significance on understanding of the nature oflife activity. In this work, the physics mechanism of diblock copolymer adsorbing on themetal crystal surface were analyzed extensively, and some interest phenomena were found.The main contents are listed as follows:（1）We used molecular dynamics simulations to study the adsorption properties ofneutral diblock copolymer on surface of face centered cubic. The effect of A-block andB-block size of number of monomers for the adsorption characteristics were studied. Whenthe total quantity of monomers of diblock copolymer chains is fixed, an increase in the number of A-block monomer will cause an increase in adsorption rate. When the number ofA-block monomer is fixed, analyze the amount of adsorption with increasing the number ofB-block monomer. It has been found that if the number of monomers in one chain is fixed, theincrease in the number of monomer A-block during adsorption would cause an increase inadsorption rate. And when the A-block monomer amount accounted for1/2of the totalamount, the maximum adsorption rate occurred. However, a further increase in the amount ofA-block monomers would cause slowly decrease in adsorption rate. For the other conditions,a fixed amount of monomer A-block with an increasing amount of B-block would result in anincrease in adsorption rate. Nevertheless, when the number of B-block A-block monomer to6times the number of monomers, the increase in the number of B-block monomer adsorptionrate will remain unchanged.（2）The adsorption mechanism of charged diblock copolymer on the surface of facecentered cubic. The effect of A-block and B-block differently charged for the adsorptioncharacteristics were studied. The result showed that charged diblock copolymer brushesstructure and counterion concentration depends on the number of A-block monomer. Themodel of diblock copolymer chains are the same as the second section, but in the case ofcounterions, at the diblock copolymer chains fixed quantity of monomer, the adsorption rateincreasing as the number of A-block monomers increases. Conversely, the number of A-blockmonomers was fixed, that the adsorption rate does not change significantly with the numberof B-block monomers increase. This shows that the number of counterions is of influence onthe adsorption at the system.（3）Reveals the adsorption mechanism of the diblock copolymer chains on thehexagonal close-packed with different stiffness of A-block or B-block. The adsorption rate ofthree different model diblock copolymers were studied, the ratio of the amount monomer ofA-block and diblock copolymer is1/2,2/3,1/3. Simultaneously, also studied the case ofA-block and B-block as flexible block respectively, the other block as semiflexible, stiff,rod-like the adsorption rate were discussed. The results showed that when the ratio of theamount monomer of A-block and diblock copolymer is1/2, the adsorption rate firstly increased and then decreased with the increasing stiffness. On the contrary, the adsorption ratefluctuated when the stiffness of B-block increases. When the ratio of the amount monomer ofA-block and diblock copolymer is2/3, the adsorption rate decreased with the increasingstiffness of A-block and then the adsorption rate remain unchanged. When the ratio of theamount monomer of A-block and diblock copolymer is1/3, the adsorption rate decreasedwhen the stiffness of A-block increases, and adsorption rate decreased and then slowlyincreased.（4）Comparison of adsorption mechanism with different potential, through therelationship between potential energy and temperature, summed up with the increase intemperature could promote the adsorption of diblock copolymer chains.（5）Study conformation changes and structural features of polyampholyte sphericalbrushes. The polyampholyte chains grafted on the spherical particles, we discussed theaverage distance of end monomers with various grafting density，charge sequence and netcharge density situations. And the final steady state conformation was obtained, the analysisof conformational properties play an important role. Proves the grafting density variations donot affect the distance of end monomers at α=1. However, when the charge sequence αdecreases, the distance of end monomers would decreases as the grafting density increased.When α=1/20and ρg=0.0442-2, the distance of end monomers reduce to minimum, even ifthe grafting density continues to rise, the distance of end monomers would not decrease. Tworadial distribution function at different grafting densities for gNmPm(r1) and gNmPc(r1),respectively. The simulation results can be clearly observed that the impact of the graftingdensity for the radial distribution functions. The impact of two radial distribution functions ofthe main factors was the various charge sequences. The charge sequence is also a major factorfor negatively and positively counterions monomer radial space distribution. Proved thegrafting density and charge sequence impact on the oscillation amplitude and oscillationperiod of net charge density curve. All of the polyampholyte chains collapsed the surface ofspherical particles, when the polyampholyte chains are flexible. However, the polyampholytechains are stiff, the conformational of the polyampholyte chains almost no change, the distance between the start and end monomers decreasing as the grafting densities increasing,at α=1/20the electrostatic attraction play a role, the increase in number of folding of thepolyampholyte chains.