Dibenzylidene Sorbitol Research Articles

Self‐Degrading Molecular Organogels: Self‐Assembled Gels Programmed to Spontaneously Liquefy after a Set Time

AbstractGels are used in the oilfield. For example, during oil recovery, organogels are pumped underground into fractures within oil‐bearing rock, so as to block fluid flow. However, after several days, the gels must be degraded (liquefied) to enable oil extraction through the fractures. To degrade gels, ‘degrading agents’ as well as external stimuli have been examined. Here, a concept is demonstrated that avoids external agents and stimuli: self‐degrading organogels based on the self‐assembly of molecular gelators. The gels are a) extremely robust (free standing solids) at time t = 0 and (b) degrade spontaneously into a sol after a set time t = tdegr that can be minutes, hours, or days. These properties are achieved by combining two readily available molecules — the organogelator (1,3:2,4)‐dibenzylidene sorbitol (DBS) and an acid (e.g., hydrochloric acid, HCl) — in an organic solvent. DBS self‐assembles into nanoscale fibrils, which connect into a 3‐D network, thereby gelling the solvent. The acid type and concentration set the value of tdegr at a given temperature. Degradation occurs because the acid slowly hydrolyzes the acetals on DBS, thereby converting DBS into small molecules that cannot form fibrils. DBS gels with a pre‐programmed “degradation clock” can be made with both polar and non‐polar organic solvents. The concept can be a game‐changer for oil recovery as it promises to make it safer, more efficient, and sustainable.

Highly Efficient and Sustainable PM Filtration Using Piezo Nanofibrous Membrane with Gradient Shrinking Porous Network

Nanofibrous filters have limited filtration against ultrafine airborne particulate matter (PM) due to thick fiber fineness and large pore size, which can be unraveled by increasing thickness and basis weight, however, the pressure drop of the filters also increases sharply. Inspired by the bryophyte leaf structure, unconventional piezo nanofibrous membranes with gradient shrinking porous network are created for PM filtration by one-step electrospinning of polyvinylidene fluoride (PVDF), dibenzylidene sorbitol (DBS), and short-chain fluorinated alkyl modified silica (F-SiO2) through pattern metallic mesh collectors. The membranes are assembled into charged and hydrophobized gradient porous networks with pores in feeding to outlet gradually shrinking. This structure features a well-designed filtration mechanism that balances filtration efficiency and pressure drop, facilitating high trap efficiency against PM (PM0.3 > 98.82%; PM0.5 > 99.87%, quality factor ∼ 0.121–0.507 Pa−1; PM0.8–7.5 = 100%) with a low pressure drop (16–55 Pa) and good stability in an acid, alkali, ultraviolet (UV), or humid environment. Simultaneously the piezo nature of the membrane endows renewable surface charge richness by hand pressing to provide sustainable caption of ultrafine particles, especially PM0.3. This study provides a new design approach for constructing PM filters in a reliable, sustainable and affordable way.

Reversed Phase-HPLC Method for Low Level Quantitation of Dimethyl dibenzylidene Sorbitol

Dimethyl dibenzylidene sorbitol (DMDBS) is one of the most commonly used nucleating agent in polypropylene formulations. In present study, a simple and robust reversed phase liquid chromatography (RP-LC) based analytical method was developed for the quantitative low-level determination of DMDBS. The best separation was achieved on a RP-HPLC column TSK gel G2000 SW, 7.5mm x 30cm, Particle Size 10 and#181;m from TOSOH Bioscience. A 0.05 M NH4AC (pH = 6.6) + 10% ACN solution was used as mobile phase at a flow rate of 1.2 ml/min. UV detection was performed at 216 nm. Retention time was found to be 13.056 min. for DMDBS. The response was a linear function of concentration over the range of 2.00 to 8.00 and#181;g/ml with correlation coefficient of 0.9996 for DMDBS. The LOD and LOQ for DMDBS were found to be 1.00 and#181;g/mL and 2.00 and#181;g/mL respectively. The method is simple, rapid and robust, which is suitable for application in quality control and can also be used for the estimation of DMDBS as a leachable/ extractable from polypropylene (PP) resin and resin products like medical device containers.

3D printing of tantalum parts based on low molecular mass organic gel system

In this study, 3D gel printing based on a low molecular mass organic gel system was employed to fabricate complex-shaped Ta parts. As opposed to a polymeric gel system, this system was initiated by heat transition. To obtain suitable printing slurry with 62 vol% solid content, 2.5 wt% resin was introduced to improve green body strength and 0.55 wt% oleic acid was added to modify the viscosity. As a result, the printed samples had relatively good surface quality without defects or pores observed on the surface. Ta particles were closely bound by dibenzylidene sorbitol (DBS) gelators. After sintering, a uniform shrinkage was obtained with a shrinkage of 11%, but the surface quality of the as sintered samples was improved. Sintering decreased the surface roughness from 4.0 μm to 2.8 μm. Besides, the as-sintered Ta samples had a relatively dense and homogenous microstructure. The relative density of the as-sintered sample was about 98%. Therefore, 3D gel printing is a promising method to prepare complex-shaped Ta parts with minimal material waste.

Polyethylene and the Nucleating Agent: Dibenzylidene Sorbitol, a Neutron Scattering Study

Dibenzylidene Sorbitol is a very effective clarification additive for isotactic polypropylene. It is not effective with polyethylene although recent studies have shown that it can act as an effective nucleating and directing agent. We employ small-angle neutron scattering measurements to more fully understand the behavior of dibenzylidene sorbitol in a polyethylene matrix. The small-aangle neutron scattering clearly shows that the disappearance of the DBS fibrils is concentration dependent and for 2% DBS the midpoint of the dissolution is at 145°C and for 1% is ~ 20°C lower

Thermoreversible gelation and self-assembly behavior of dibenzylidene sorbitol in ternary solvent mixtures

The self-assembly behavior of 1,3:2,4-dibenzylidene-D-sorbitol (DBS) in ternary solvents has been systematically investigated for the use of kerosene gel in the aerospace propulsion. DBS forms a yield viscoelastic gels in a wide range of kerosene/hexanol/DMSO solvent concentrations despite the fact that DBS is incapable of gelling kerosene fuel. The gelation behavior of DBS in the solvent mixture is predicted using the Hansen solubility parameters. The polar parameter (δP) and hydrogen bonding (δH) parameter lie in the range of 1.96 ≤ δP ≤ 4.30 J0.5cm−1.5 and 3.40 ≤ δH ≤ 7.30 J0.5cm−1.5 respectively for the formation of gel in kerosene/hexanol/DMSO system. The phase transition temperature (Tf) of DBS gel is determined using temperature sweep measurement and predicted using modified Friedrich (MF) relation which is found be in close agreement with an average deviation of ± 10 °C. However, the deviation becomes larger when δP > 4.30 and δH > 7.30, in other words, with increase in the solvent polarity. As the solvent polarity or concentration of hexanol increases in the mixture, the gels exhibit a low Tf and $$ {G}_{max}^{\prime } $$ value because of the hindrance of self-assembling ability of DBS due to the intermolecular hydrogen bonding between DBS and solvents. The viscoelastic behavior of DBS gels is investigated using the oscillation sweep measurements and the storage modulus G′ is found to be higher than the loss modulus G″ for larger stress amplitude and frequency, indicating a solid-like nature of the gels. Furthermore, the microstructure analysis shows the presence of 3D nano-fibrillar morphology, which further depends on the solvent polarity. Microstructure changes from ‘rope-like’ fiber aggregate (Hex100; CH = 88 wt%) to a ‘web-like’ structures (Hex25; CH = 25 wt%), when the CH is decreased in the solvent mixture.

Orthogonal Templating Control of the Crystallisation of Poly(ε-Caprolactone).

The crystal growth of poly(ε-caprolactone) can be very effectively directed through the use of small amounts of dibenzylidene sorbitol in conjunction with modest flow fields to yield extremely high levels of the preferred polymer crystal orientation. We show that by introducing small quantities of a terpolymer, based on polyvinyl butyral we can switch the symmetry axis of the final lamellar orientation from parallel to perpendicular to the melt flow direction. During shear flow of the polymer melt, the dibenzylidene sorbitol forms highly extended nanoparticles which adopt a preferred alignment with respect to the flow field and on cooling, polymer crystallisation is directed by these particles. The presence of the terpolymer, based on polyvinyl butyral, limits the aspect ratio of the dibenzylidene sorbitol (DBS) particles, such that the preferred orientation of the particles in the polymer melt changes from parallel to normal to the flow direction. The alignment of lamellar crystals perpendicular to the flow direction has important implications for applications such as scaffolds for tissue engineering and for barrier film properties.

Effect of Sorbitol Templates on the Preferential Crystallographic Growth of Isotactic Polypropylene Wax

The crystallization of isotactic polypropylene wax (iPP) in the presence of different sorbitol structures was studied. Dibenzylidene Sorbitol (DBS), as well as two of its derivatives with one or two methyl groups in the DBS molecule (MDBS and DMDBS, respectively), were tested as nanometer-size fibrillar templates. The early nucleation stage and crystal morphology were analyzed in Real-Time Wide-Angle X-ray Scattering (WAXS) and polarized optical microscopy (POM). It was found that the iPP crystals showed an α-phase unit cell for the three different sorbitols. However, a preferential crystal growth in the plane (040) was observed for iPP–MDBS. The macrostructure morphology of the iPP–DBS and iPP–DMDBS wax compounds was spherulitic, while nodular macrocrystals were observed for the iPP–MDBS compound. It was concluded that the MDBS template promoted a lower interface energy because of its match with the c-axis of the iPP wax crystals, whereas, in the case of the DBS and DMDBS templates, the preferential plane was the (110), characteristic of the iPP spherulitic arrangement.

Crystallization induced enhancement on electrical conductivity and strength of highly conductive PP composites

A highly conductive and reinforced polypropylene/nickel coated glass fiber (PP/NCGF) composite is fabricated via a simple and efficient strategy. Nucleating agent induced crystallization leads to the sharp volume excluded effect and drives NCGFs into the amorphous region of PP matrix, thus the formation of conductive network connected by NCGFs is promoted remarkably. The incorporation of nucleating agent dibenzylidene sorbitol (DBS) improves the strength of composites simultaneously due to the enhanced crystallinity and the reinforced interfacial interaction. Accordingly, the percolation threshold of PP/NCGF composites is decreased to 0.35 vol% (Ni content) by loading DBS, and the conductivity increases by four order of magnitude around the percolation threshold which exceeds 70 S/m with the Ni content of only 0.47 vol%. The tensile strength of PP/NCGF composites is increased by about 30–40 % in all range of NCGF content. This exciting result provides a strategy to prepare high-performance conductive composites by crystallization-induced enhancement.

Self-assembly behavior of gels composed of dibenzylidene sorbitol derivatives and poly(ethylene glycol)

The strongest intermolecular interactions between DBS molecules in the DBS/PEG systems led to the more regular structure compared with the DMDBS/PEG and TBPMN/PEG systems.

Competition between α and β Crystallization in Isotactic Polypropylene: Effect of Nucleating Agents Composition

Abstract Based on the different nucleation ability, different contents and proportions of the mixed nucleating agents were melt compounded with pure isotactic polypropylene resins employed in this work, selective β nucleating agent was a compound of pimelic acid and calcium stearate, the α nucleating agent was a type of dibenzylidene sorbitol derivative. The competition attributed to the different type of interactions between a nucleating agent and isotactic polypropylene molecular chains during crystallization was investigated in this research. For a low content of the mixed nucleating agents used, α nucleation dominated the crystallization behavior of isotactic polypropylene, while with an increase of the content of the mixed nucleating agents, the situation was reversed and β nucleation became dominant. In the β dominated region, both of the molecular chain and segmental motions were various with different nucleating agent proportion. Thus, the content and proportion of the components of the nucleating agents were the critical factors in the competition during crystallization.

Investigations on Carboxy Dibenzylidene Sorbitol Hydrogels Using EPR Spectroscopy

Low-molecular-weight organic gelators generate physical gels by the formation of three-dimensional fibrous network structures as a response to various physicochemical stimuli such as heat, light, ultrasound and chemical environments. Dibenzylidene sorbitol (DBS) represents a typical compound able to generate gels because of some prerequisite structural features: the presence of functional groups to form intermolecular hydrogen bonds and of aromatic groups to be involved in π–π interactions, or chirality. Herein, we present the synthesis of three derivatives of DBS-bearing carboxy groups attached to phenyl rings and the corresponding spin-labelled compounds. We studied the formation of physical gels resulting from self-assembly of DBS derivatives with the aim of highlighting the influence of the position of the carboxy group on the gel properties. These types of compounds can form gels in polar solvents (such as water, DMSO) by either temperature treatment or variation of the pH. In this study, the systems were investigated by rheological measurements, SEM analysis and EPR measurements. The results showed that the introduction of carboxy groups into the structure of DBS generates weaker gels compared with the parent gelator, DBS. The spin probes used in this study (spin-labelled DBS derivatives and 5-doxyl stearic acid) demonstrated that assembly of gelator molecules is a highly selective process. The two-component feature of EPR spectra of spin probes in gels is proof that EPR spectroscopy is sensitive to the non-homogeneity of these systems.

Gelation of Oil upon Contact with Water: A Bioinspired Scheme for the Self-Repair of Oil Leaks from Underwater Tubes.

Molecular organogelators convert oils into gels by forming self-assembled fibrous networks. Here, we demonstrate that such gelation can be activated by contacting the oil with an immiscible solvent (water). Our gelator is dibenzylidene sorbitol (DBS), which forms a low-viscosity sol when added to toluene containing a small amount of dimethyl sulfoxide (DMSO). Upon contact with water, DMSO partitions into the water, activating gelation of DBS in the toluene. The gel grows from the oil/water interface and slowly envelops the oil phase. We have exploited this effect for the self-repair of oil leaks from underwater tubes. When a DBS/toluene/DMSO solution flows through the tube, it forms a gel selectively at the leak point, thereby plugging the leak and restoring flow. Our approach is reminiscent of wound-sealing via blood-clotting: there also, inactive gelators in blood are activated at the wound site into a fibrous network, thereby plugging the wound and restoring blood flow.

Maximum bubble pressure rheology of low molecular mass organogels.

Maximum bubble pressure rheology is used to characterize organogels of 0.25 wt % 12-hydroxystearic acid (12-HSA) in mineral oil, 3 wt % (1,3:2,4) dibenzylidene sorbitol (DBS) in poly(ethylene glycol), and 1 wt % 1,3:2,4-bis(3,4-dimethylbenzylidene) sorbitol (DMDBS) in poly(ethylene glycol). The maximum pressure required to inflate a bubble at the end of capillary inserted in a gel is measured. This pressure is related to the gel modulus in the case of elastic cavitation and the gel modulus and toughness in the case of irreversible fracture. The 12-HSA/mineral oil gels are used to demonstrate that this is a facile technique useful for studying time-dependent gel formation and aging and the thermal transition from a gel to a solution. Comparison is made to both qualitative gel tilting measurements and quantitative oscillatory shear rheology to highlight the utility of this measurement and its complementary nature to oscillatory shear rheology. The DBS and DMDBS demonstrate the generality of this measurement to measure gel transition temperatures.

Preparation of polyethylene microporous membranes with high water permeability from thermally induced multiple phase transitions

Thermally induced phase separation (TIPS) has been widely used to prepare microporous membrane. The interaction and dynamic asymmetry between polymer and solvent sometime make the transition happen through viscoelastic phase separation (VPS) mechanism. Under such condition, cell like structure is obtained with low water permeability. In this paper, a new method is proposed to obtain high permeability membranes by TIPS. Dibenzylidene sorbitol (DBS) and HDPE-g-MAH are introduced into the polyethylene/di-iso-decyl phthalate (HDPE/DIDP) system, which exhibits an upper critical solution temperature (UCST) behavior and undergoes VPS mechanism during cooling. DBS can self-assemble and form fibril network both in HDPE and DIDP. The addition of HDPE-g-MAH makes DBS mainly distributed in HDPE-rich domains, while it mostly locates in the DIDP-rich domain in the ternary system due to their similar polarity. The self-assembly of DBS in the HDPE-rich domains can induce the secondary liquid–liquid phase separation, which significantly change the structure in walls between cells. High permeability of pure water and high retention of permeability in silica suspension can be obtained under proper control of the extent of these phase transitions.

On row-structures in sheared polypropylene and a propylene–ethylene copolymer

The crystallisation of polymers such as polyethylene or polypropylene from the melt is greatly influenced by the flow-thermal history prior to the crystallisation. We explore the influence of the chemical configuration of polypropylene based chains on the formation of row structures on crystallisation. We use a combination of in situ time resolved small-angle X-ray scattering, ex situ wide angle X-ray scattering with optical and scanning electron microscopy to show that row nuclei are formed in random copolymers of propylene with a limited amount of ethylene subjected to modest shear flow fields. We contrast observations performed using two homopolymers of isotactic polypropylene and one random copolymer of propylene and ethylene. We propose that it is not strictly necessary to argue that the row nuclei are already crystalline nor to invoke epitaxial crystallisation as the mechanism for the nucleation of lamellae, as similar structures can be formed on carbon nanotubes and fibrils of dibenzylidene sorbitol. The combination of microscopy and scattering provides a powerful approach to investigating these phenomena, especially as compared to either technique used in isolation.

Accelerated Crystallization of Poly(lactic acid): Synergistic Effect of Poly(ethylene glycol), Dibenzylidene Sorbitol, and Long-Chain Branching

The crystallization of poly(lactic acid) (PLA) is usually slow and related to the content of d-lactide. A new approach is suggested in this work to accelerate the crystallization of PLA via the synergistic effect of nanofibril nucleating agent (dibenzylidene sorbitol, DBS), plasticizer (poly(ethylene glycol), PEG) and long-chain branching in PLA. It is found that premade DBS/PEG gel can act as an active nucleating agent of PLA, which makes the crystallization peak appear during cooling. The preparation of DBS/PEG gel before mixing with PLA is important because self-assembly of DBS directly in PLA melt is difficult even in the presence of PEG. The mixing temperature is also found to be critical, which determines the amount of residual nanofibrils after melt mixing. Tuning the chain structure into long-chain branching via multifunctional monomer pentaerythritol triacrylate (PETA) will further speed up the crystallization of PLA because of the additional interaction between DBS nanofibrils and the grafted monomers. It is proven that the acceleration of crystallization is not ascribed to the change of crystal form but is due to the dominating increase in the nucleation density as well as the faster growth rate of spherulites in the presence of the plasticizer. Therefore, the problems of low melt strength and slow crystallization of PLA can be solved simultaneously via the present approach.

Preparation and characterization of novel poly(vinylidene fluoride) membranes using self-assembled dibenzylidene sorbitol for membrane distillation

We proposed a method for the preparation of novel poly(vinylidene fluoride) (PVDF) membranes with self-assembled 1,3:2,4-di(3,4-dimethylbenzylidene) sorbitol (DMDBS). The vapor-induced phase separation (VIPS) method with a dry/wet process was used to produce DMDBS/PVDF composite membranes. The resulting membranes exhibited the coexistence of PVDF cellular pores and crystalline particles. The DMDBS molecules self-assembled into nanofibril structures, and a large number of nanofibrils were found on the surfaces and in the cross-sections of the prepared membranes. The DMDBS nanofibril networks in the PVDF matrix acted as reinforcing materials that enhance the hardness and stiffness of the membranes. Moreover, because of the entangled DMDBS networks, a greater strain was required to induce sample failure; therefore, the ductility of the membranes increased with increasing amounts of DMDBS. In addition, in a membrane distillation process, our composite membranes exhibited a good permeate flux that was comparable to that of commercial PVDF membranes.

Molecular Self-Assembly Assisted Liquid–Liquid Phase Separation in Ultrahigh Molecular Weight Polyethylene/Liquid Paraffin/Dibenzylidene Sorbitol Ternary Blends

Dibenzylidene sorbitol (DBS) was chosen as an in situ forming nucleating agent to study ultrahigh molecular weight polyethylene (UHMWPE)/liquid paraffin (LP) physical gel and complex phase separation. The experimental results indicated that DBS self-assembled into fibrils first and the solution became a physical gel before liquid–liquid phase separation (LLPS) and crystallization during thermally induced phase separation (TIPS) of UHMWPE/LP/DBS solution. The temperature of DBS self-assembly and viscoelasticity of UHMWPE/LP/DBS gel show a strong dependence on DBS concentration, temperature, and time. By controlling the relative quenching depth and annealing time, the grow rate of the characteristic length showed a crossover from LLPS to crystallization, which was further justified by differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD). With decreasing temperature further, crystallization occurred with the aid of DBS fibrils. Those interactions were affected mutually, showed comp...

Solvents effects in the formation and viscoelasticity of DBS organogels

The gel behavior of dibenzylidene sorbitol (DBS) in different solvents was studied by rheology, optical microscopy and transmission electron microscopy. It was found that DBS molecules would self-assemble into fibrils with a helical structure, and the fibrillar diameter decreased with increasing solvent polarity. The gel dissolution temperature was extremely sensitive to the DBS concentration and solvent polarity, which could be explained by the Gibbs–Thomson equation through interfacial stress. The phase diagram, which classified the sol, the gel and the cluster regime in different solvents was determined by rheology and optical microscopy. The critical gel concentration was found to increase as the difference in the polar and hydrogen-bonding components of the solubility parameter (Δδph) between the gelator and solvents decreased. Meanwhile, the difference in the critical gel concentration in different solvents could explain the difference in the relaxation exponent and the gel strength at the gel point well. In the stable gel state, the plateau modulus depended on the gelator concentration according to a power-law scaling, GoN ∝ c2, which was consistent with entanglement theory and independent of the type of solvent. However, the gelator–solvent interaction and its temperature dependence were found to affect the stability of the gel substantially under large amplitude oscillatory shear. The critical strain would increase as Δδph decreased, and showed more evident temperature dependence on solvents with a smaller Δδph.