The diffusion kinetics of a molecular probe—rhodamine B—in ternary aqueous solutions containing poly(vinyl alcohol), glycerol, and surfactants was investigated using fluorescence correlation ...spectroscopy and dynamic light scattering. We show that the diffusion characteristics of rhodamine B in such complex systems is determined by a synergistic effect of molecular crowding and intermolecular interactions between chemical species. The presence of glycerol has no noticeable impact on rhodamine B diffusion at low concentration, but significantly slows down the diffusion of rhodamine B above 3.9% (w/v) due to a dominating steric inhibition effect. Furthermore, introducing surfactants (cationic/nonionic/anionic) to the system results in a decreased diffusion coefficient of the molecular probe. In solutions containing nonionic surfactant, this can be explained by an increased crowding effect. For ternary poly(vinyl alcohol) solutions containing cationic or anionic surfactant, surfactant—polymer and surfactant—rhodamine B interactions alongside the crowding effect of the molecules slow down the overall diffusivity of rhodamine B. The results advance our insight of molecular migration in a broad range of industrial complex formulations that incorporate multiple compounds, and highlight the importance of selecting the appropriate additives and surfactants in formulated products.
Abstract
Formulations based on poly(hydroxybutyrate) (PHB) and poly(hydroxybutyrate‐
co
‐valerate) were studied to statistically assess the importance of process parameters (temperature) and ...chemistry in filled and/or plasticized PHB‐based formulations on spherulite growth rate (SGR) and nucleation density (ND). It was found that in binary systems, addition of a plasticizer results in shift of the maximum SGR towards lower temperatures, with the value of the shift dependent on polymer‐plasticizer compatibility. The presence of the filler does not significantly influence SGR, instead resulting in ND changes dependent on filler chemistry, with Cloisite Ca
++
showing the strongest nucleating action in all formulations among fillers studied. In ternary systems, statistical analysis shows that SGR strongly depends on the crystallization temperature (T
c
), plasticizer type and concentration, and hydroxyvalerate content in the polymer chain while being independent of the presence and chemistry of the filler in the system. ND has, however, proven to be dependent on all investigated parameters, including both filler type and its concentration, with T
c
being the most important factor. These results expand the understanding of factors controlling crystallization in polymer systems and provide an initial set of design tools that can be used to control mechanical properties in new generations of packaging materials.
We investigated the diffusion characteristics of a molecular probe in organic films of poly(vinyl alcohol) (PVA) that replicate formulations used as packaging materials. Diffusion kinetics of ...Rhodamine B (RhB) was measured in thin films of PVA containing glycerol and surfactants of various headgroup chemistry (cationic/nonionic/anionic) using fluorescence recovery after photobleaching and atomic force microscopy. Here we show how diffusion is determined by both molecular arrangement within the film and the nature/magnitude of intermolecular interactions. Addition of glycerol could improve the flexibility of PVA chains initially but imposed steric inhibition once the concentration exceeded the threshold of 44 wt%. In all investigated formulations, RhB exhibited diffusion-coupled mechanism. The presence of surfactants (at 6 wt%) reduced the diffusivity of RhB in PVA matrix for all types of surfactants used (by 30 %, 61 %, and 88 % for cationic, nonionic, and anionic surfactant addition compared to control sample, respectively). We conclude that steric inhibition effects underpin the diffusion of RhB in PVA thin films doped with nonionic surfactant. However, for PVA films with the addition of cationic or anionic surfactant, interactions between surfactant and fluorophore are likely responsible for the change in diffusivity of the molecular probe.
•Diffusion kinetics of molecular probes in thin PVA films were quantified as a function of the composition.•The nature and magnitude of migration are determined by both molecular arrangement and intermolecular interactions.•Adding glycerol to PVA film could increase the migration of the molecular probe initially, but will reduce it above 44 wt%.•Presence of surfactants would decrease the diffusivity of the molecular probe.
Complex formulations based on poly(hydroxybutyrate) (PHB) and poly(hydroxybutyrate-
co
-valerate) (PHBV) were studied to statistically assess the effect of formulation (i.e., hydroxyvalerate (HV) ...content, plasticiser chemistry and content, filler type and content) on their thermal properties and degree of crystallinity (
X
c
). In binary systems, thermal properties were mainly influenced by filler type rather than its content, while for plasticised systems the changes were dependent on both increasing plasticiser content and PHB-plasticiser compatibility. Variations in HV content affected the ability of the polymer chain to fold, leading to significant changes in both thermal properties and
X
c
. In ternary systems, presence of multiple additives and consequent changes in intermolecular interactions lead to multifaceted behaviours that were not easily predicted by results from binary systems alone. For example, melting temperature did not show dependence on filler presence in PHBV systems despite introducing variations in pure PHB systems. In general, thermal properties and
X
c
are affected by all parameters studied, with changes in system free volume (i.e. changes in HV content and plasticisation) playing the most significant role. These results expand the understanding of factors controlling crystallisation in complex polymer systems and can be used to control matrix properties in new generations of packaging materials.
The wetting kinetics of poly(vinyl alcohol) (PVA)-based films by water was investigated using contact angle (CA) goniometry, Fourier-transform infrared spectroscopy, and atomic force microscopy. We ...show that CA evolution is determined by four main factors: film composition, preparation method, presence of plasticiser in the matrix, and relative humidity (RH) conditions during aging. All formulations prepared from partially hydrolysed polymer were less susceptible to dissolution compared to fully hydrolysed counterparts, with the CA evolution character shifting from exponential to linear for respective formulations. This behaviour is likely attributed to the intrinsic properties of PVA matrices, i.e. changes in free volume, tortuosity, as well as size and distribution of crystalline regions. Incorporation of glycerol as a plasticiser results in overall faster CA evolution, with surface spreading playing more significant role compared to non-plasticised samples. Furthermore, aging of PVA-based films does not lead to profound changes in any environment except 100% RH. For these conditions, the initial stages of PVA dissolution due to water absorption were observed, with the changes in the matrix continuity dependent on PVA degree of hydrolysis. These results expand on the understanding of initial stages of polymer dissolution in consumer goods products and can pave the way to enhanced performance and prolonged shelf life of the products.
•Surface wetting kinetics of PVA-based films by water was captured and described quantitatively.•Partially hydrolysed PVA films show an exponential decrease in contact angle (CA) over time with a large decrease in overall CA values; fully hydrolysed PVA films, however, show slow, linear CA evolution with overall small changes in CA values.•Introducing glycerol to PVA formulations results in plasticisation of the films, leading to drastic changes in wetting kinetics.•Aging PVA at low relative humidity (<50 % RH ) does not seem to affect wetting behaviour, while high RH significantly changes physcial appearance and wetting kinetics of the PVA films.
Understanding migration of small molecules within polymer matrices (either additives already in the matrix or those infiltrating from adjacent media) is a challenge in many industrial systems. ...Migration can lead to undesirable changes in product properties, reduced shelf-lives and increased material wastage that is harmful for the environment. Herein, this challenge is addressed by studying the migration characteristics of model additives (surfactants of various head group chemistry, plasticiser, and fluorophore) in poly(vinyl alcohol) (PVA) films that are widely used in single unit detergent applications. The aim of this project is to investigate how lateral migration (x,y-migration) and vertical migration (z-migration) of small molecules affect film behaviour, establishing the mechanisms that influence this phenomenon, the molecular interactions associated, and their timescales. To fully address the complex, multi-component nature of PVA-based films, complexity was introduced stepwise into the system. First, the migration mechanisms of a model additive (rhodamine B, RhB) were tracked through aqueous solutions of PVA, glycerol (a plasticiser) and surfactants of various head group chemistry (cationic, nonionic, and anionic) using fluorescence correlation spectroscopy. Specific intermolecular interactions and steric effects were revealed to be the primary factors influencing migration in formulations containing ionic surfactants and nonionic surfactants, respectively. Presence of the plasticiser was shown to decrease the diffusivity of the tracer, chiefly due to increased viscosity in the system. These solutions were then spin-coated, and RhB diffusion through the resultant films was tracked using fluorescence recovery after photobleaching. In films, an additional mechanism of migration was identified - compatibility of the components in the system, with phase separation of glycerol from the PVA matrix lowering the overall tracer diffusivity; again, intermolecular interactions and steric effects controlled tracer diffusivity in the surfactant-doped systems. Third, the mechanism of surfactant migration was studied as films were aged under various environmental conditions (primarily relative humidity, RH). The plasticising effect of atmospheric water was demonstrated, with films restructuring to reach equilibrium molecular conformation. The nature and speed of the restructuring was dependent on surfactant concentration and its compatibility with the other components of the system. The properties of the PVA-based matrix were then measured upon exposing it to elevated temperature, with system compatibility overall increasing as the glass transition temperature was exceeded. A significant dependence on compatibility was observed while changing the properties of the matrix (increased degree of hydrolysis (DH) and molecular weight (Mw) of the polymer) as well as introducing a second surfactant to the system. However, the molecular arrangement of surfactant within the polymer matrix remained the same independent of polymer DH and Mw. Overall, observed changes could be explained by the compatibility of the four components with one another, their hydrogen bonding, and other intermolecular interactions in the system. Finally, wetting of PVA-based film by water, dodecane, or aqueous surfactant solutions of various head group chemistry were examined. Variations in solvophilic behaviour were observed upon changing the polymer crystallinity, crystallite size, size of the free volume cavities, and polymer entanglement, regardless of liquid medium. Further, matrix hydrophilicity was identified as an important factor controlling infiltration of surfactant solutions into the polymer matrix. Through this work, importance of environmental conditions and chemical environment on molecular migration is highlighted, providing a set of variables that need to be controlled while designing migration in industrially relevant systems as well as future directions for further investigations.
In the presented experiments the carbonation process in multiphase system was carried out using the reactor with rotating discs. Calcite was produced by controlled fast precipitation through gaseous ...carbon dioxide adsorption in calcium hydroxide slurry with the constant discus revolution speed rate equal to 120 r min−1. Initial concentration and volume of the slurry was equal to 23 mM l−1 or 54 mM l−1 and 1 l or 2 l, respectively. The size of monodispersed single crystals precipitated in the aqueous solution was strongly dependent on the process parameters and varied (scanning electron microscope pictures, ImageJ Programme calculation) from 90 nm to 320 nm. To explain the way of single calcite crystal nucleation and growth the simulation of the crystals formation has been performed. This simulation bases on the new model, which takes into account kinetics of the multiphase reaction, crystals nucleation and their growth. Crystal morphology data obtained during the precipitation process have been compared with the model simulation results. The internally consistent model very well describes formation of the calcite nanoparticles and can be used and recommended for accurate calculation of the particle and aggregates size as well as their distribution in the reactor.
Skeletal muscles are postulated to be a potent regulator of systemic nitric oxide homeostasis. In this study, we aimed to evaluate the impact of physical training on the heart and skeletal muscle ...nitric oxide bioavailability (judged on the basis of intramuscular nitrite and nitrate) in rats.
Rats were trained on a treadmill for 8 weeks, performing mainly endurance running sessions with some sprinting runs. Muscle nitrite (NO
) and nitrate (NO
) concentrations were measured using a high-performance liquid chromatography-based method, while amino acids, pyruvate, lactate, and reduced and oxidized glutathione were determined using a liquid chromatography coupled with tandem mass spectrometry technique. The content of muscle nitrite reductases (electron transport chain proteins, myoglobin, and xanthine oxidase) was assessed by western immunoblotting. We found that 8 weeks of endurance training decreased basal NO
in the locomotory muscles and in the heart, without changes in the basal NO
. In the slow-twitch oxidative soleus muscle, the decrease in NO
was already present after the first week of training, and the content of nitrite reductases remained unchanged throughout the entire period of training, except for the electron transport chain protein content, which increased no sooner than after 8 weeks of training.
Muscle NO
level, opposed to NO
, decreases in the time course of training. This effect is rapid and already visible in the slow-oxidative soleus after the first week of training. The underlying mechanisms of training-induced muscle NO
decrease may involve an increase in the oxidative stress, as well as metabolite changes related to an increased muscle anaerobic glycolytic activity contributing to (1) direct chemical reduction of NO
or (2) activation of muscle nitrite reductases.
This study aimed at investigating the effects of 2, 4 and 8 weeks of endurance training on the contractile properties of slow (S), fast fatigue resistant (FR) and fast fatigable (FF) motor units ...(MUs) in rat medial gastrocnemius (MG) in relation to the changes in muscle mitochondrial biogenesis. The properties of functionally isolated MUs were examined in vivo. Mitochondrial biogenesis was judged based on the changes in mitochondrial DNA copy number (mtDNA), the content of the electron transport chain (ETC) proteins and PGC-1α in the MG. Moreover, the markers of mitochondria remodeling mitofusins (Mfn1, Mfn2) and dynamin-like protein (Opa1) were studied using qPCR. A proportion of FR MUs increased from 37.9% to 50.8% and a proportion of FF units decreased from 44.7% to 26.6% after 8 weeks of training. The increased fatigue resistance, shortened twitch duration, and increased ability to potentiate force were found as early as after 2 weeks of endurance training, predominantly in FR MUs. Moreover, just after 2 weeks of the training an enhancement of the mitochondrial network remodeling was present as judged by an increase in expression of Mfn1, Opa1 and an increase in PGC-1α in the slow part of MG. Interestingly, no signs of intensification of mitochondrial biogenesis assessed by ETC proteins content and mtDNA in slow and fast parts of gastrocnemius were found at this stage of the training. Nevertheless, after 8 weeks of training an increase in the ETC protein content was observed, but mainly in the slow part of gastrocnemius. Concluding, the functional changes in MUs' contractile properties leading to the enhancement of muscle performance accompanied by an activation of signalling that controls the muscle mitochondrial network reorganisation and mitochondrial biogenesis belong to an early muscle adaptive responses that precede an increase in mitochondrial ETC protein content.
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