Complex fluid polymer liquids

Soft condensed-matter materials, such as complex fluids (polymer solutions and melts, microemulsions, gels, and liquid crystals), which are characterized by the existence of one or more mesoscopic length scales. 

Complex liquids are ubiquitous in materials manufacture. In some cases, they are formed and must be handled at intermediate steps in the manufacture of materials (e.g., sols and gels in the making of ceranucs, mixtures of monomer and polymer in reactive processing of polymers). In other cases (e.g., composite liquids), they are the actual products. Understanding the properties of complex fluids and the imphcations of fluid properties for the design of materials processes or end uses presents a formidable intellectual challenge. 

Rheology deals with the deformation and flow of any material under the influence of an applied stress. In practical apphcations, it is related with flow, transport, and handling any simple and complex fluids [1], It deals with a variety of materials from elastic Hookean solids to viscous Newtonian liquid. In general, rheology is concerned with the deformation of solid materials including metals, plastics, and mbbers, and hquids such as polymer melts, slurries, and polymer solutions. 

In the previous sections, theories were reviewed where the optical properties of polymer liquids were cast in terms of the microscopic properties of the constituent chains. The dynamics of polymer chains subject to external fields that orient and distort these complex liquids are considered in this section for a variety of systems ranging from dilute solutions to melts. Detailed descriptions of theories for the dynamics and structure of polymer fluids subject to flow are found in a number of books, including those by Bird et al. [62], Doi and Edwards [63], and Larson [64],... 

Deuterium NMR (2H NMR) has been used extensively to study and characterise molecular properties in various complex fluids such as liquid crystals [1, 2, 3] and in polymer systems [4]. 

Perhaps the most important distinction between classical solids and classical liquids is that the latter quickly shape themselves to the container in which they reside, while the former maintain their shape indefinitely. Many complex fluids are intermediate between solid and liquid in that while they maintain their shape for a time, they eventually flowr They are solids at short times and liquids at long times hence, they are viscoelastic. The characteristic time required for them to change from solid to liquid varies from fractions of a second to days, or even years, depending on the fluid. Examples of complex fluids with long structural or molecular relaxation times include glass-forming liquids, polymer melts and solutions, and micellar solutions. 

Finally, there are complex fluids that are intermediate between solid and liquid in more than one of the ways listed above. Liquid crystalline polymers (LCPs) are both viscoelastic and liquid crystalline. Ordered block copolymers are viscoelastic and anisotropic. Glassy polymers possess long viscoelastic time scales both because they are glassy and because they are polymeric. Filled polymer melts possess the properties of both polymer melts and suspensions. 

The rheological and flow properties of ordered block copolymers are extraordinarily complex these materials are well-deserving of the apellation complex fluids. Like the liquid-crystalline polymers described in Chapter 11, block copolymers combine the complexities of small-molecule liquid crystals with those of polymeric liquids. Hence, at low frequencies or shear rates, the rheology and flow-alignment characteristics of block copolymers are in some respects similar to those of small-molecule liquid crystals, while at high shear rates or frequencies, polymeric modes of behavior are more important. 

The anticipated developments in neutron sources and instrumentation will provide exciting new opportunities for the study of polymers, soft matter, and complex fluids. Rather than try to cite specific detailed examples, broad areas of potential exploitation and current trends will be highlighted. The examples described in the earlier section of this paper indicate a distinct trend towards the study of complex multi-component or multi-phase systems, the use of complex environments (flow, pressure, confinement), the study of complex interfaces (for example, liquid-liquid interface), and non-equilibrium in situ studies. 

Enormous effort is spent on studying complex fluids, more-so than any of the previous topics reviewed above. These fluids include polymer solutions and melts, alkanes, colloidal systems, electrolytes, liquid crystals, micelles, surfactants, dendrimers and, increasingly, biological systems such as DNA and proteins in solution. There are therefore many specialist areas and it is impossible to review them all here. As such, we sample only a select few areas that reflect our own personal interests, and apologise to readers who have specific interests elsewhere. First, we briefly look over some simulations on colloidal systems, alkanes, dendrimers, biomolecular systems, etc, and will then... 

In spite of this, it is perhaps useful to briefly consider the conditions at solid boundaries and fluid interfaces for complex/non-Newtonian fluids. One reason for doing this is that it provides additional emphasis to the idea from the proceeding paragraphs that there will be conditions when the commonly applied no-slip condition breaks down. It should be stated, at the outset, that the question of slip or no-slip is still a matter of current research interest for complex fluids. Nevertheless, the occurrence of sbp is generally accepted to be much more common for complex/non-Newtonian fluids than for Newtonian/small molecule liquids. In the latter case, we have seen that slip generally involves either extreme shear stresses or solid walls that exhibit extremely weak attractive interactions with the hquids, and the issue is primarily one of basic scientific interest. Polymer melts, on the other hand, commonly exhibit apparent manifestations of slip that play a critical role in the success or failure of certain types of commercial processing applications.43... 

The constant of proportionality in equation 2.10 is the viscosity of the liquid tf). Some fluids, such as water, olive oil and sucrose solutions obey this equation and are said to be Newtonian. Their viscosity does not depend on the velocity gradient, i.e. how fast the liquid is sheared - known as the shear rate, More complex fluids (e.g. solutions of polymers) have a viscosity that does depend on the shear rate. Such fluids are called non-Newtonian . Many complex fluids, for example tomato ketchup and ice cream mix, become less viscous when they are sheared and are described as shear-thinning . Tapping the bottom of the bottle applies shear to the ketchup, which becomes less viscous and flows more easily onto your plate. Other fluids, such as a concentrated solution of cornstarch or quicksand, become more viscous (i.e. they are shear-thickening ). Experiment 7 in Chapter 8 gives some examples of non-Newtonian fluids. A single viscosity is not sufficient to describe the flow properties of non-Newtonian liquids and if a viscosity is stated, the shear rate at which it was measured must also be given. 

The thermodynamic behavior of fluids near critical points is drastically different from the critical behavior implied by classical equations of state. This difference is caused by long-range fluctuations of the order parameter associated with the critical phase transition. In one-component fluids near the vapor-liquid critical point the order parameter may be identified with the density or in incompressible liquid mixtures near the consolute point with the concentration. To account for the effects of the critical fluctuations in practice, a crossover theory has been developed to bridge the gap between nonclassical critical behavior asymptotically close to the critical point and classical behavior further away from the critical point. We shall demonstrate how this theory can be used to incorporate the effects of critical fluctuations into classical cubic equations of state like the van der Waals equation. Furthermore, we shall show how the crossover theory can be applied to represent the thermodynamic properties of one-component fluids as well as phase-equilibria properties of liquid mixtures including closed solubility loops. We shall also consider crossover critical phenomena in complex fluids, such as solutions of electrolytes and polymer solutions. When the structure of a complex fluid is characterized by a nanoscopic or mesoscopic length scale which is comparable to the size of the critical fluctuations, a specific sharp and even nonmonotonic crossover from classical behavior to asymptotic critical behavior is observed. In polymer solutions the crossover temperature corresponds to a state where the correlation length is equal to the radius of gyration of the polymer molecules. A... 

Soft matter science is nowadays an acronym for an increasingly important class of materials, which encompasses polymers, liquid crystals, molecular assembhes building hierarchical structmes, and the whole area of colloidal sciences. Common to all of them is that fluctuations and thus the thermal energy T and the entropy play an important role. Soft then means that these materials are in a state of matter that are neither simple liquids nor hard solids of the type studied in hard condensed matter, hence sometimes soft matter firms also under the name complex fluids. 

Pang JN, Owens RG, Tacher L, Parriaux A (2006) A numerical study of the SPH method for simulating transient viscoelastic free surface flow. J Non-Newtonian Fluid Mech 139 68-84 Feng J, Leal LG (1997) Simulating complex flows of liquid crystalline polymer using the Doi theory. J Rheol 41 1317—1335... 

This transition from a homogeneous towards a nonhomogeneous flow has been reported in complex fluids of various microstructure such as lyotropic micellar and lamellar phases [44,121,122], triblock copolymers solutions [123,124], viral suspensions [125], thermotropic liquid crystal polymers [126], electro-rheological fluids [127], soft glassy materials [128], granular materials [129,130], or foams [131-133]. 

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