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![1. ' Fringed micelle' model of the crystalline-amorphous structure of PC polymers. [24]](profile/Harry-Levine/publication/301564755/figure/fig19/AS:406609491709952@1473954665060/Fringed-micelle-model-of-the-crystalline-amorphous-structure-of-PC-polymers-24.png)
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Interest in water will continue to grow for a long time to come. It will continue to spread over a large number of disciplines and technologies. Research into water in all its aspects has become so diverse that even those with a direct interest find it impossible to keep up with the original literature beyond a very limited range. On the other hand...
Citations
... Polyamide, indeed, displays a strong tendency to absorb water from the environment. The absorbed water acts as a plasticizer: water molecules increase polymeric chains mobility [17], thereby implying a significant drop of the polymer mechanical properties [18]. ...
The knowledge of the mechanical behavior of a 3D-printed material is fundamental for the 3D printing outbreaking technology to be considered for a range of applications. In this framework, the significance, reliability, and accuracy of the information obtained by testing material coupons assumes a pivotal role. The present work focuses on an evaluation of the static mechanical properties and failure modes of a 3D-printed short carbon fiber-reinforced polyamide in relation to the specimen’s unique meso-structural morphology and water content. Within the manufacturing limitations of a commercially available printer, specimens of dedicated combinations of geometry and printing patterns were specifically conceived and tested. The specimens’ meso-structure morphologies were investigated by micro-computed tomography. The material failure mechanisms were inferred from an analysis of the specimens’ fracture surfaces and failure morphologies. The outcomes of the present analysis indicate that each test specimen retained proper mechanical properties, thereby suggesting that they should be accurately designed to deliver representative information of the underlying material beads or of their deposition layout. Suggestions on the adoption of preferred test specimens for evaluating specific material properties were proposed.
... Moisture-induced plasticization decreases the glass transition temperature (T g ), hampering the material's elastic behavior and, consequently, losing integrity [9,10]. Therefore, structural composites should be employed at temperatures lower than their T g range. ...
... Whenever there is a shift from the glassy state to the rubbery state or vice versa in a material, thermodynamic properties, molecular mobility, dielectric constant, and mechanical properties also change (Sperling 1986). The factors influencing this transition are plasticization by water, weight of ingredients, and the amount and type of bonding interactions (Levine and Slade 1988). Plasticization of films due to water results in decline of glass transition temperature of amorphous hydrocolloids. ...
The stability of food products depends upon the type of packaging used for their containment. The overuse of synthetic polymers has originated serious environmental issues in past years. To curb this, alternate packaging materials made from the biological materials are being adopted in food industries. One type of these packaging films is based upon the polysaccharides, which are hydrophilic in nature. Thus, the moisture migration from the foods packaged in these films is needed to be analyzed using modeling equations. Diffusion is the primary phenomenon responsible for mass transfer through these films, and its rate is influenced by food as well as surrounding conditions. Considering this, models are conceptualized on the basis of food, package type, and its properties and environmental conditions. Sorption is a common process of gaining (adsorption) and loosing moisture (desorption) until equilibrium is attained in processed foods. Models like Guggenheim, Anderson, and de Boer (GAB) and Brunauer, Emmett, and Teller (BET) are widely used to describe the behavior of foods under constant temperature and relative humidity. Transpiration and respiration processes are common with the fresh produce. Theoretical and gravimetric approaches explain the moisture migration behavior through films due to transpiration. In respiration modeling, Arrhenius equation describes the temperature dependency, and enzyme kinetics explains inhibition due to carbon dioxide on respiration rates. These models either single or in combinations are helpful in determining moisture transfer through polysaccharide-based films for one or multicomponent foods.
... Constitutive models have also been developed to simulate the rate-dependent response and post-yield softening in tension [16,17,19], however these models did not attempt to distinguish shear plasticity from craze yielding in their phenomenological description. The plasticising effect of water on the physical properties of polymers is also well known [20,21]. The blending of small molecules with long polymer chains increases the chain mobility [22][23][24]. ...
... The blending of small molecules with long polymer chains increases the chain mobility [22][23][24]. Water molecules can also break intermolecular bonds, further leading to increased chain mobility [20,21,25]. The increase in chain mobility in turn leads to a decrease in the glass transition temperature [22,26,27], and a reduction in elastic modulus and yield stress [8,22,27]. ...
... The difference between the first and second heating curves in wet samples is attributed to the presence of water. The decrease in glass transition temperature 1 is a manifestation of the plasticising effect of water, which increases the segmental mobility of the chains and triggers primary structural relaxation at lower temperature [20]. Glass transition in wet samples is immediately followed by a narrow endothermic overshoot, which increases as the immersion time increases. ...
... T g is a characteristic value for each substance, and it decreases at lower molecular weights (MW). Moreover, as was presented i.e. by Levine & Slade [9] , water is the most ubiquitous plasticizer in the world, due to its very low T g (about À135 C). The data presented by Sablani et al. [10] indicated that the presence of a certain amount of water has more plasticizing effect on products rich in sugar. ...
... Te results of impact tests indicate that the impact strength of the specimens increased after water ageing ( Figure 10) due to the plasticization efect of water. Previous studies showed that water is used as a crystallizing plasticizer [45]. In addition, plasticized composite specimens exhibited higher impact strength than nonplasticized composite specimens after water ageing. ...
... Tis can be due to the fact that water plasticizes plasticized composites more than nonplasticized composites, that is, the glass transition temperature of plasticized composites drops when immersed in water for a prolonged time, which leads to an increase in plasticization. Furthermore, the water plasticization efect is higher for crystalline materials than for amorphous materials [45]. It is a fact that plasticized polymers are more crystalline than neat polymers due to the crystallization efect of plasticizers [46]. ...
Biocomposites are promising candidates for some engineering applications owing to the growing environmental and economic challenges to replace petrochemical-based polymers with biodegradable polymers. Herein, sisal fiber reinforced polylactic acid (PLA) composite specimens were fabricated using an injection molding machine with and without plasticizer. The weight percentage (wt%) of the sisal fiber varied between 5% and 20%. The effect of the sisal fiber wt% on water absorption resistance and mechanical properties was investigated experimentally using water ageing, mechanical, and morphological studies. The results revealed that tensile and flexural specimens after water ageing exhibited lower tensile and flexural strengths with higher water absorption behavior at 20 wt% sisal fiber than 5 wt% sisal fiber, while the impact strength increased after water ageing. In addition, the sisal fiber/PLA composites exhibited higher water absorption behavior and lower strength and modulus at 20 wt% sisal fiber after water ageing. Moreover, the water absorption decreased with the incorporation of the plasticizer.
... Water transport during hydration in these matrices changes their initial equilibrium into the neither equilibrated nor homogenous state. The increasing water content within the matrix plasticizes polymeric chains and increases their mobility [7]. Most theoretical and experimental approaches simplify the problem [8], while the phenomena occurring during the hydration of such systems are complex [9][10][11][12][13]. ...
Hypothesis:
Three-dimensional 1H UltraShort Echo Time magnetic resonance imaging (1H 3D UTE MRI) of the matrix tablet made of hydrophilic polymer hydrated in heavy water (D2O) will allow investigation of the hydration-induced spatiotemporal evolution of the material originally included in the matrix tablet during manufacturing (i.e., polymer chains and bound water).
Experiments:
The oblong-shaped sodium alginate matrix tablets were used to verify the hypothesis. The matrix was measured before and during hydration in D2O for up to 2 h using the 1H 3D UTE MRI. Five echo times (first at 20 μs) were used, resulting in five three-dimensional images (one image for each echo time). In chosen cross-sections, two parametric images, i.e., amplitude and T2* relaxation time maps, were calculated using "pixel-by-pixel" mono-exponential fitting.
Findings:
The regions of the alginate matrix with T2* shorter than 600 μs were analyzed before (air-dry matrix) and during hydration (parametric, spatiotemporal analysis). During the study, only hydrogen nuclei (protons) pre-existing in the air-dry sample (polymer and bound water) were monitored because the hydration medium (D2O) was not visible. As a result, it was found that morphological changes in regions having T2* shorter than 300 μs were the effect of fast initial water ingress into the core of the matrix and subsequent polymer mobilization (early hydration providing additional 5% w/w hydration medium content relating to air-dry matrix). In particular, evolving layers in T2* maps were detected, and a fracture network was formed shortly after the matrix immersion in D2O. The current study presented a coherent picture of polymer mobilization accompanied by local polymer density decrease. We concluded, that the T2* mapping using 3D UTE MRI can effectively be applied as a polymer mobilization marker.
... Water-insoluble hydrophobic polymers containing polar groups also have moderate water content, which is suggested to be a good indicator of the biocompatibility of plastics [145]. Undoubtedly, water as a plasticizer depresses the glass tran-sition temperature (T g ) of polymers and increases the flexibility [146,147]. Because hydration can increase the free volume of polymer and might also break/weaken the polymer-polymer interaction network, thus increasing the polymer flexibility and enhancing entropic contributions. ...
The stealth effect plays a central role on capacitating nanomaterials for drug delivery applications through improving the pharmacokinetics such as blood circulation, biodistribution, and tissue targeting. Here based on a practical analysis of stealth efficiency and a theoretical discussion of relevant factors, we provide an integrated material and biological perspective in terms of engineering stealth nanomaterials. The analysis surprisingly shows that more than 85% of the reported stealth nanomaterials encounter a rapid drop of blood concentration to half of the administered dose within 1 h post administration although a relatively long β-phase is observed. A term, pseudo-stealth effect, is used to delineate this common pharmacokinetics behavior of nanomaterials, that is, dose-dependent nonlinear pharmacokinetics because of saturating or depressing bio-clearance of RES. We further propose structural holism can be a watershed to improve the stealth effect; that is, the whole surface structure and geometry play important roles, rather than solely relying on a single factor such as maximizing repulsion force through polymer-based steric stabilization (e.g., PEGylation) or inhibiting immune attack through a bio-inspired component. Consequently, engineering delicate structural hierarchies to minimize attractive binding sites, that is, minimal charges/dipole and hydrophobic domain, becomes crucial. In parallel, the pragmatic implementation of the pseudo-stealth effect and dynamic modulation of the stealth effect are discussed for future development.
... The initial loss of material is interpreted as alcohol diffusion and extraction of various soluble components, such as initiators, plasticisers and unreacted residual monomers [20,57]. A diffusant liquid and voids left from extracted components may cause an increase in the free volume, which can lead to weakening or breaking of polymer bonds [58]. This mechanism is potentially responsible for further weight loss in isopropanol. ...
... The NMR MOUSE data of ethanol are better understood when interpreted along with microscopic images and weight changes. The initial loss of material is attributed to ethanol diffusion and component leaching that creates voids in the PMMA [58]. This increase of free volume enables additional solvent to be absorbed and diffused in the polymer. ...
... At this point, it is worth mentioning that an increase in free volume could also lead to depolymerisation [58], that is, dissolution of PMMA. This could not be verified here, but the formation of crazing sustains this hypothesis: PMMA has occasionally displayed cracking on dissolution, and crazing seen here always precedes cracking [22,56]. ...
Exposure of heritage plastics to solvents can cause several changes to their surface layers and bulk. The amorphous nature of certain plastics, particularly polymethyl methacrylate (PMMA), allows penetration and diffusion of low-molecular liquids, which can lead to swelling, cracking, plasticisation or stiffening, extraction and dissolution of polymer and additive components. Such phenomena compromise the visual characteristics, chemical and physical structure of heritage collections and remain, for the most part, unexplored. Research studies present contradicting evidence concerning the use of solvents and their safe application on PMMA. The main discrepancy is about PMMA being permeable to water or not. Alcohols have also triggered debates about whether they cause leaching and/or depolymerisation. This paper investigates the potential effects that selected free polar and non-polar solvents—employed in different media as cleaning systems—can have on PMMA after prolonged contact. The Hildebrand solubility theory was used to select solvents based on PMMA’s miscibility. The effects of deionised water, ethanol, isopropanol and petroleum ether are examined through a 30-day immersion study of PMMA via microscopic examination, weight change measurements, ATR-FTIR, peak height ratios, and NMR MOUSE. All four solvents extracted soluble components, i.e. unreacted residual monomer, and increased PMMA’s surface sensitivity to abrasions. Water and petroleum ether did not cause any measurable chemical or physical changes. Alcohols caused surface crystallisation and crazing, with isopropanol leading to stiffening and ethanol to plasticisation of the material. These effects, although extreme and absent in most routine cleaning timeframes, demonstrate the cumulative damage these solvents can potentially induce to PMMA.
... Moisture absorption usually causes degradation of mechanical properties of composites, especially matrix-and interface-dominated properties, such as interlaminar, in-plane shear and transverse tensile strengths. This loss in mechanical properties can be attributed to main phenomena such as matrix plasticization [85][86][87][88], matrix (or fiber) hydrolysis [18,56,88] and swelling [9,73,89,90]. ...
... Plasticization leads to increased intermolecular space or free volume, and may involve the weakening or breaking of selective intermolecular bonds [86], leading to a higher mobility to the polymer chains, with decrease in stiffness and increase in deformability, with consequent loss of mechanical properties [41]. Plasticization can be indirectly evaluated from the decrease in the glass transition temperature (T g ) and many works have shown the occurrence of this phenomenon with hygrothermal aging [9,56,75,85,88,[91][92][93]. ...
