Multiscale Rheological Research On Multiphase Polymer Complex Fluids

Generally speaking, the property of polymer is viscoelastic, and its structure is multiscale, so polymer is a kind of complex fluid. The structure and flow behavior of high performance polymer materials made by blending are more complex. Therefore, the theory and experiment of polymer do not reach the level of seamless connection from macroscale to microscale. To realize closely relating the single molecule design to material processing, the research on mesoscale is a part of crucial works. The rheological research considering multiscale interaction and the development of constitutive equation are closely related to the structure, processing and performance of materials. Therefore, they are very meaningful both in theory and practice.In this article, the research objects are multiphase polymer complex fluids including viscoelastic polymer solution, melt and filled polymer system. In the sense of scale, macroscopic melt flow, mesoscopic droplet and morphology, and nanoscale filler are all connected together.Drop deformation, breakup and coalescence are helpful to the basic understanding of the dispersion in polymer blending, so four-roll mill, the instrument suitable for the research of drop dynamics, is built in our laboratory. The development, structure, principle and application of four-roll mill are introduced. Different Newtonian, NonNewtonian fluids and sample systems combined mutually by them are investigated. In the extension, shear or complex flow fields, the drop deformation and relaxation characterization are obtained and systematic experimental data are supplied for the development of constitutive equation which bridges the mesoscale and macroscale. It is experimentally found that the drop deformation of Newtonian system is determined by viscosity ratio between drop and matrix and capillary number. The addition of high molecular weight component causes the elasticity increase and steady drop deformation decrease. Meanwhile, the process of drop relaxation can be divided into two stages which dominated by interfacial tension and elasticity respectively.The constitutive model, introduced by Yu et al, is evaluated. This model can embody the integration of meso-scale and macro-scale. It is verified that Yu et al's Model is effective for Newtonian matrix whether the drop is Newtonian fluid or not in small deformation region, the deviation appear in large deformation region. The case is also if the drop is Newtonian and matrix is NonNewtonian fluid. However, when the two phases are also viscoelastic fluids, more work should be done to descript the long relaxation mode.A new coalescence process of meso-scale viscoelastic drop is found with four-roll mill by iterative elongation and relaxation. In general case, the coalescence of Newtonian drops includes matrix film formation, drainage, rupture and merge four stages. It is difficult to breakup and coalescence for viscoelastic drops. The drop used is mainly low molecular weight polyisobutylene (PIB) containing high molecular weight polyisobutylene (HPIB). The matrix is polydimethyl siloxane (PDMS). After iterative elongation and relaxation, the drop turns into the dumbbell like structure bead-string-bead (BSB). The elastic force from stretched molecules in the string pulls the two beads approach overcoming the viscous drag of matrix, the relaxed molecules in the string drainage to beads under the Laplace force, then the string diameter keeps constant and the two beads coalescence to one drop.According to the balance among Laplace force on the interface, viscous drag of matrix and the elastic force in the string, a model is derived to descript the BSB phenomenon, which is agree with experiment reasonably. The factors affecting the string diameter are relative to both microscopic material parameter and macroscopic process parameter which are unified into one formula. The rule and regime of BSB phenomenon happening is illustrated. The difference and transformation from beads-on-string which appear in jet or stretching rheometer are discussed. BSB phenomenon is inspiring for the orientation and entanglement state of polymers and the nonlinear drop dynamic in multiphase system.The linear and nonlinear rheological properties and morphology observation are carried out for the different composition blends of polypropylene (PP) and metallocene catalyzed ethelene-octene copolymer (POE). If the blend morphology is sea and island, then Palierne model can be used to simulate the drop diameter, the fit results are very close to the direct observation. KBKZ model, powerful for polymer melt, can be used to descript PP/POE blends of all composition, and the effect of interfacial morphology on model parameter is discussed too.The appearance of solid-like phenomenon of Polymer/clay nanocomposites melt is regarded as the sign of nano effect. It is found that the appearance of solid-like phenomenon is not necessary the indication of the percolation of clay slice in the melt. The dynamic storage modulus G' increase at high temperature in air may be the result of silicate participated chemical network came into being by the crosslinkage of polymers initiated by oxygen diffusion from free sample surface. The crosslinkage mechanism is also explored. This phenomenon should be noticed and avoided in the preparation and processing of polymer/clay nanocomposites.