Aggregates of chains

The structure formation in an ER fluid was simulated [99]. The characteristic parameter is the ratio of the Brownian force to the dipolar force. Over a wide range of this ratio there is rapid chain formation followed by aggregation of chains into thick columns with a body-centered tetragonal structure observed. Above a threshold of the intensity of an external ahgn-ing field, condensation of the particles happens [100]. This effect has also been studied for MR fluids [101]. The rheological behavior of ER fluids [102] depends on the structure formed chainlike, shear-string, or liquid. Coexistence in dipolar fluids in a field [103], for a Stockmayer fluid in an applied field [104], and the structure of soft-sphere dipolar fluids were investigated [105], and ferroelectric phases were found [106]. An island of vapor-liquid coexistence was found for dipolar hard spherocylinders [107]. It exists between a phase where the particles form chains of dipoles in a nose-to-tail... 

Fig. 37 Linear chain formation of DNA-coated paramagnetic polystyrene colloids with the different self-protection schemes displayed in Fig. 33. By using an external magnetic field, DNA-functionalized particles were brought together into linear chains, after which the temperature was lowered below the association temperature for beads, and the field turned off. (a) Representative microscopy picture of the resulting chain structures immediately after switching off the magnetic field, (b-d) Chains after 1 h at the specified temperature for particles functionalized with sticky end sequences able to form both loops and hairpins (b, c) or only loops (d). The degree of aggregation of chains in (d) is intermediate between the unprotected, branched chains in (b) and the perfectly linear, protected chains in (c). Adapted with permission from [157]...

Polystyrene beads assembled into chains, aggregates of chains, and 2D arrays in a ferromagnetic fluid in the presence of an external magnetic field Magnetic forces pm 56... 

Celluloses are similar to other linear polymeric materials in that they can possess one-dimensional order within an individual chain as well as three-dimensional order within an aggregate of chains. Increments in the levels of order occur during the isolation of native celluloses and also as a result of exposure to conditions that promote molecular mobility, such as elevated temperatures and immersion in plasticizing fluids. These increments generally result in embrittlement of the cellulosic materials. Similar effects are expected to occur upon aging of cellulosic textiles and papers over extended periods, and may be accelerated by hydrolytic cleavage of cellulosic chains. The implications of these effects for conservation practices, both with respect to recovery of function as well as in the assessment of deterioration, are reviewed. 

Among the other parameters able to induce similar macroscopic effects, the addition of divalent cations is particularly effective. Literature data are in almost complete agreement with the view that an aggregation of chains induced by ions is responsible for the gel forma-... 

Such chains are insoluble in all other media (including water ) this results in the aggregation of chains to form primary particles. 

Sophisticated experimental methods allow the development of models for polymers in dilute and semi-dilute solutions. Chain stiffness may be represented by the Kuhn segment lengths and determined in dilute solution. Models for cellulose and cellulose derivatives have recently been published whose main features are the irreversible aggregation of chains, if hydrogen bonding is possible even in dilute solutions. Trisubstituted cellulose derivatives or cellulose in hydrogen bond breaking solvents exist as molecular dispersed chains. How-... 

The mesomorphic forms of sPP [29,267], sPS [268,269] and sPPMS [270] are characterized by chains in ordered trans-planar conformations packed in small disordered aggregates, which maintain the structural features of one of the polymorphic forms of the polymers, only up to very short distances. In the case of sPS and sPPMS, the small aggregates of chains are characterized by packing modes very close to those of the a form of sPS [268,269] and form III of sPPMS [270]. 

Three dimensional simulations of strongly interacting DHS in an external field are less extensive but give qualitatively similar results, including aggregation of chains [170]. At large values of the dipole moment high potential... 

Aggregation of chains occurs in solutions with c < 1 wt% Physical thermoreversible gels are formed from solutions annealed below room temperature gels melt upon heating above their 7 ... 

Whether RNA is a branched molecule still remains unknown. The evidence indicates a linear, highly asymmetric molecule capable of fiber formation. If there are any branches they are short. The RNA particle apparently grows by aggregation of chains rather than branching as in the ramified glycogen molecule. 

In very concentrated solutions and in the amorphous solid film of polyethylene terephthalate some local parallel aggregation of chain segments must have been present. 

A kinetic theory of fracture intends to interrelate the motion and response of molecules to the ultimate properties of a stressed sample. A kinetic theory, therefore, entails a molecular description of the deformation of the microscopically heterogeneous and anisotropic aggregates of chains to such an extent that critical deformation processes can be identified. The macroscopic deformation of any aggregate potentially involves the deformation, displacement, and/or reorientation of so different substructural elements as bond vectors, chain segments or crystal lamellae. 

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