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Vibration Damping by Polymers
Published in Asit Baran Samui, Smart Polymers, 2022
Bikash Chandra Chakraborty, Praveen Srinivasan
When a polymer chain is not undergoing any net displacement or flow as a whole, even then the segments can undergo reptation type of motion. This segmental mobility freezes below Tg, at which temperature the polymer undergoes the transition from a soft rubbery state to the stiff glassy state upon cooling. The term glass transition originated from glass which is an amorphous supercooled liquid and becomes soft at a particular temperature. The glass transition phenomenon is exhibited by only the amorphous phase of a polymer.
Passive transport in the interstitium and circulation: basics
Published in Benjamin Loret, Fernando M. F. Simões, Biomechanical Aspects of Soft Tissues, 2017
Benjamin Loret, Fernando M. F. Simões
The formula (15.5.1) introduces the size of the diffusing species through its molar mass and the formula (15.5.2) view them as spheres. This approximation is questionable for diffusing species whose shape departs significantly from the sphere. The reptation theory considers flexible polymer chains like DNA whose diffusion is constrained by entanglement points (fixed obstacles) representing the gel chains. During diffusion of the polymer by brownian motion, the obstacles appear as forming a sort of tube. Lateral motion of the diffusant can take place only at the extremities of the tube while its central part moves essentially along the tube. As for the diffusion coefficient D∼1/m^α, with m^ the molar mass of the polymer, two regimes are distinguished according to the ratio of the length of the polymer chains versus the tube size. For a small ratio (short chains), the behavior is said Rouse-like and α ∈ [0.5, 1], while, for a large ratio > 10 (long chains), the reptation model corresponds to α ∈ [2, 3].
Elements of Polymer Science
Published in E. Desmond Goddard, James V. Gruber, Principles of Polymer Science and Technology in Cosmetics and Personal Care, 1999
E. Desmond Goddard, James V. Gruber
the chain is assumed to be contained in a hypothetical tube placed in the network. The “knots” in the network are seen as obstacles around which the chain must “wriggle” during translation. Two types of motions can be envisaged: (1) conformational changes within the confines of the tube; and (2) reptation, a snake-like motion that translates the chain within the tube until it finally escapes at the tube end (Fig. 8). The theory of reptation has been applied with large success to develop theories describing the dynamics and viscoelastic properties of entangled polymers.
The role of thermodynamics and kinetics in rubber–bitumen systems: a theoretical overview
Published in International Journal of Pavement Engineering, 2021
Haopeng Wang, Panos Apostolidis, Jiqing Zhu, Xueyan Liu, Athanasios Skarpas, Sandra Erkens
As discussed previously, polymer chains will disentangle if contacted with thermodynamically compatible solvents. Disentanglement occurs in a form of diffusional motions of chains out of the swollen polymer gel. The disentanglement of polymer chains can be described by the famous reptation model (De Gennes 1971). In the reptation model, an entangled chain diffuses along its confining tube as shown in Figure 11. The time needed for the chain to diffuse out of its original tube is the reptation time . It is predicted to be proportional to the square of the chain size (radius of gyration) divided by the reptation diffusion coefficient (Equation (20))In the context of CRMB system, it is important to know the rubber dissolution rate in bitumen to control the binder properties. The dissolution rate is related to the disentanglement rate of the polymer chain, which is taken to be proportional to the chain size divided by the reptation time. ThusIt is reported that and can be related to polymer molecular weight and concentration (Papanu et al.1989). Therefore, the disentanglement rate of rubber in bitumen can be expressed aswhere A is an empirical constant; is the molecular weight of rubber; a is related to the rubber molecular weight distribution and b is related to rubber concentration. Both a and b are larger than 1.
Surgical applications of intracorporal tissue adhesive agents: current evidence and future development
Published in Expert Review of Medical Devices, 2020
Nicholas Gillman, David Lloyd, Randy Bindra, Rui Ruan, Minghao Zheng
Chain entanglement refers to a polymers ability to tangle with other polymer chains. The force of adhesion/cohesion between polymers is highly determined by the length of the polymer chain, known as the reptation model [24]. Position-dependent chain motion toward the chain ends also influences the confinement of the polymers [25]. Increasing the flexibility of a polymer chain allows for greater interpenetration and entanglement [26].