Viscoelasticity and Dynamics of Confined Polyelectrolyte/Layered Silicate Nanocomposites: The Influence of Intercalation and Exfoliation

Macro Chemistry & Physics

2018

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Nanoclays are 2D silicate structures with spatial periodicity and relatively constant gallery separation d 001 of the order of 1 nm. Hence, these nanoparticles offer naturally confining environments to macromolecules, especially in an intercalated state. It is believed that the macromolecular nanoconfinement found in intercalated morphologies of polymer-clay nanocomposites, would be largely responsible for the changes of thermomechanical properties. [8] It is known that confinement can induce lowering or increasing of the glass transition temperature, T g , in small molecule glassy materials, [9] in glassy polymers, [10][11][12] and in polymer nanocomposites. [6][7][8]13,14] The influence of confinement has also been evidenced in rheological properties when analyzing ultrathin films of polydimethyl siloxane. [15] Confinement has also induced changes to crystallization and crystalline structure of hybrid nanocomposite networks. [16,17] Confinement in polymer nanocomposites occurs when 1) polymer chains are constrained between layered silicates, [1,7,8] 2) polymer chains are inside nanopores or nanocylinders, [18,19] or 3) inorganic nanoparticles and hybrids (i.e., silica, alumina, POSS, and so on) dispersed in a polymer matrix where polymer fractions would have reduced mobility due to being tightly bound to the nanoparticles or in highly confined regions between closely packed nanoparticles. [13,14,[20][21][22][23] Additional to the topological confinement condition the polymer dimensions also dictate the degree of confinement. Hence, 2R < d defines a weak confined system whereas 2R >> d defines a strongly confined system, where R is the polymer dimension (e.g., radius of gyration or hydrodynamic radius) and d is the pore diameter or gallery spacing, as depicted in Scheme 1. [24][25][26] Finally, polymer-solid interface (nanoparticle) interactions which can be attractive or repulsive play a prominent role defining the properties in a nanocomposite; [23,26] the picture is quite complex.Model polymeric systems mimicking confined environments based on ultrathin films have been investigated to explain the behavior of the glass transition temperature T g . [27][28][29][30][31][32] Nanostructured films obtained from grafted nanoparticles (gold or SiO 2 ) dispersed in a polymeric solution have also been studied to understand the influence of nanoparticle-matrix interactions on the thermal properties (tuning the length of the grafted chains promoted or not interactions with the polymer Nanocomposites This research investigates confinement-induced dynamics retardation behavior in intercalated acrylic/clay nanocomposites. Nanostructured waterborne latex contains up to 3 wt% nanoclay, and transmission electron microscopy shows well-dispersed intercalated morphology. Dynamics in the melt is analyzed using the time-temperature superposition principle. Confinement induces dynamics retardation, and the entanglement relaxation time τ e increases over an order of magnitude. The cooperative motion retardation also reduces viscous d...

Section: Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Viscoelasticity and Dynamics of Intercalated Polymer/Bentonite Nanocomposites

Macro Chemistry & Physics

2018

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Polyhedral Oligomeric Silsesquioxane Induced Thermomechanical Reinforcement in Polymer Films Using Only Parts‐per‐Million Content

Lichtenhan

2020

Macro Materials & Eng

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particle dispersion. The tendency of nano particles to agglomerate has been an unsurpassed hurdle so far. [2,3] The decora tion of nanoparticles surfaces with specific end groups or oligomers to induce homo geneous dispersion and particlepolymer matrix interactions is a cost and time consuming alternative with unconvincing results. [4] Controlling the dispersion of nano particles in a polymeric matrix is key to understand their influence on physical properties. Enabling the dispersion at near unitlevel takes advantage of the high surface area and volume of nano particles and particlelike nanochemicals. Under this condition, recent experimental evidence suggests that only small nano particle content (<5 wt%) is required to produce nanoeffects. [5-10] On the other hand, recent research has shown that when nanoparticles are present in a polymeric matrix, at low con centrations and welldispersed, [7-10] con finement effects can become relevant and the chain dynamics can be modified. [11,12] Therefore, dispersed silica nanoparticles produced entanglement dilation and reduced the melt viscosity of the polymer matrix. [8,13-18] On the other hand, welldispersed layer silicates in polyacrylates and polyelectrolytes significantly attenuated the αrelaxation and increased by orders of magni tude the tensile mechanical modulus by confining the macro molecules between the nanoplatelets. [7,19] There was, however, a penalty on strain at fracture as the nanoparticles acted as stress concentrators thus reducing the extensibility of the nano composite, a result typically seen in reinforced (nano) com posites, i.e., the improvement of tensile mechanical properties degrades performance in extensibility. [7,20] There is, therefore, the notion that confinement induced by welldispersed nanoparticles can induce significant changes to the physical properties of a matrix, and this has been investi gated in model systems [21] in an effort to understand the unu sual properties of materials produced by nature. [22] There is, however, the question of the number of nanoparticles present in the matrix. Recently, the authors reported on a methodology to dis perse untethered polyhedral oligomeric silsesquioxanes (POSS) at a single unit in a lowdensity polyethylene (LDPE) Reinforcement of polymers by nanoparticles has been a challenge due to aggregation and solubility limits, especially at high loads. In this research, a robust and environmentally friendly fabrication approach to produce films reinforced with only parts-per-million (ppm) octamethyl-polyhedral oligomeric silsesquioxane (mePOSS) using conventional extrusion and blow molding processing is demonstrated. The nanocomposites exhibit enhanced thermomechanical properties, and only 160 ppm mePOSS increase the tensile mechanical modulus, E, by ≈120% relative to the neat polymer. Remarkably, there is no penalty on strain at fracture ε f , as usually seen in reinforced (nano) composites. Toughness, yield stress, tear, and puncture resistance are also an increasing function of mePOSS content. F...

Parts‐per‐million polyhedral oligomeric silsesquioxane loading induced mechanical reinforcement in polyethylene nanocomposites. When small and well‐dispersed yields big

Polymers for Advanced Techs

Lichtenhan

Reyes‐Mayer³

et al. 2020

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The expectation that composites fabricated with nanoscale reinforcing materials will exhibit exceptional mechanical properties remains to be fulfilled. Here, octaisobutyl‐polyhedral oligomeric silsesquioxane (buPOSS) nanochemical was melt blended with low‐density/linear low‐density polyethylene (LDPE/LLDPE) to form nanostructured films. We demonstrate that buPOSS concentrations of only 80 to 400 parts‐per‐million (ppm) are enough to produce nearly 2‐fold increase of the film's tensile Young's modulus, EMD. Strikingly, there was no penalty on strain at fracture εf,MD, as usually seen in reinforced (nano) composites, rather εf,MD increased with buPOSS content. Furthermore, other important mechanical properties like toughness, yield stress, tear resistance, and dart impact strength were also an increasing function of buPOSS content. The dispersion of buPOSS into the polyethylene matrix at nearly single cage unit is the key to mechanical reinforcement. The buPOSS size D, smaller than the virtual tube diameter dt defined by Doi and Edwards, indicate that buPOSS is capable to intercalate the entangled macromolecules and mechanically reinforce without acting as stress concentrators. Furthermore, the entanglement intercalation and consequent reduction of free volume induced reduction of oxygen transmission (OTR) through the films and the barrier properties were intact after 18 months aging at room temperature. The nanosized and efficient dispersion of buPOSS is key to the mechanical reinforcement at only ppm loading and these results add a new paradigm to polymer nanocomposites formulation.