Smart Film Research Articles

Recent Advances in the Development of 1,4-Cyclohexanedimethanol (CHDM) and Cyclic-Monomer-Based Advanced Amorphous and Semi-Crystalline Polyesters for Smart Film Applications.

Polyester-based advanced thin films have versatile industrial applications, especially in the fields of textiles, packaging, and electronics. Recent advances in polymer science and engineering have resulted in the development of advanced amorphous and semi-crystalline polyesters with exceptional performance compared to those of conventional polymeric films. Among these, 1,4-cyclohexanedimethanol (CHDM) and cyclic-monomer-based polyesters have gained considerable attention for their exceptional characteristics and potential applications in smart films. This review article provides a comprehensive overview of the recent advances in the synthesis, characterization, and applications of CHDM and cyclic-monomer-based advanced polymers for smart film applications. It discusses the structure-property relationships of these innovative polyesters and highlights their unique characteristics, including thermal, mechanical, and barrier characteristics. Furthermore, this article also emphasizes the solution, melt, and solid-state polymerizations of the polymers. Special emphasis is placed on the influence of the addition of a second diol or second diacid on the performance characteristics of synthesized polyesters/copolyesters to explore their versatile industrial applications. Additionally, the impact of the stereochemistry of the monomers is explored to optimize the characterization of polyesters suitable for industrial applications. Furthermore, this article explores the potential of these advanced polyesters to be considered as materials for smart film applications, especially in the field of flexible electronics. Finally, this article examines the challenges and future recommendations for the development of CHDM and cyclic-monomer-based polyesters for smart film applications. It discusses potential avenues for further research, including in-depth studies for the synthesis and characterization of polyesters, the development of sustainable and biodegradable alternatives to cyclic monomers, alternative green approaches for the synthesis of polymers, etc. This review article provides valuable insight for researchers in academia and industry who are working in the fields of polymer science and materials engineering.

The electrically controlled dimming film of thiol-vinyl ether system with low-voltage and high contrast ratio for smart windows

As a type of smart window, polymer dispersed liquid crystal (PDLC) electrically controlled dimming film can respond to external electrical stimuli to regulate the optical flux of sunlight, reducing energy consumption. Herein, a PDLC film was prepared by systematically studying the functionalities and structural compatibility of vinyl ether and thiol compounds, and the optimal PDLC film possesses a superior contrast ratio (CR) of 196.9. When the film thickness is adjusted to 8 μm, the film saturation voltage is reduced to 6.7 V, still maintaining a high CR of 48.4. The well-designed PDLC films exhibited excellent modulation of light. The temperature difference between PDLC film and bare ITO glass can reach 4 °C under the simulated sunlight test, demonstrating the good thermal insulation performance. This smart films with low power consumption and high CR can meet the demand for active regulation of optical flux on smart windows.

Monitoring fish freshness with pH-sensitive hydrogel films containing quercetin or eucalyptol

This research developed pH-sensitive smart films using carboxymethyl cellulose (CMC) and collagen (COL), combined with either quercetin (QCT) or eucalyptol (EUC), to prevent fish meat spoilage. COL, extracted from isinglass, was confirmed as type I through SDS-PAGE. The films were characterized using FESEM, FTIR, and TGA. The addition of QCT or EUC enhanced antioxidant levels to 60.16% and 70.83%, respectively, up from a baseline of 10.4%. It also increased tensile strength from 3.32 ± 0.22 to 11.8 ± 0.25 and 13.2 ± 0.27 MPa, and enhanced elongation at break from 5 ± 3.1% to 27.7 ± 1.1% and 30.15 ± 2.1%. Fish meat packaged with QCT showed a lower spoilage rate due to the antibacterial and antioxidant effects of EUC and QCT (TVBN = 7.37 ± 0.01), compared to CMC/COL film (TVBN = 10.11 ± 0.02) and non-packaged fish (TVBN = 11.23 ± 0.01). The films exhibit >80% transparency, highlighting their suitability for food packaging. CMC/COL/QCT is preferred for fish packaging because it offers better mechanical properties and lower TVB-N levels.

Highly stable and multifunctional intelligent film based on grape skin anthocyanin, polyvinyl alcohol, chitosan and selenopeptide: Preparation, characterization and application

Highly stable and multifunctional intelligent films were fabricated using a combination of grape skin anthocyanin, polyvinyl alcohol, chitosan and selenopeptide, and the influence of selenopeptide concentration on films' properties and their effectiveness in strawberry preservation and freshness monitoring was investigated. The results showed that the incorporated selenopeptide could interact with polyvinyl alcohol and grape skin anthocyanin via hydrogen bonding, improving the hydrophobic, UV-blocking, and mechanical characteristics of the films. In particular, the introduction of 0.4% selenopeptide into the film notably boosted its tensile strength from 11.91 MPa to 26.91 MPa. More importantly, the films incorporated with selenopeptide showed decent antioxidant and antibacterial properties, along with high storage stability and thermal stability. Adding 0.4% selenopeptide to the film can increase the shelf life of strawberries at 25 °C by 3 days, and a distinct color change showing fair good linear relationship with the freshness indexes of the strawberry (hardness and weight loss rate) was observed. Overall, anthocyanin-infused films combined with selenopeptide have demonstrated promising results in preserving food and monitoring freshness, opening up new opportunities for preparing stable, smart and active films.

Multiple Chirality Switching of a Dye‐Grafted Helical Polymer Film Driven by Acid & Base

AbstractA stimuli‐responsive multiple chirality switching material, which can regulate opposed chiral absorption characteristics, has great application value in the fields of optical modulation, information storage and encryption, etc. However, due to the rareness of effective functional systems and the complexity of material structures, developing this type of material remains an insurmountable challenge. Herein, a smart polymer film with multiple chirality inversion properties was fabricated efficiently based on a newly‐designed acid & base‐sensitive dye‐grafted helical polymer. Benefited from the cooperative effects of various weak interactions (hydrogen bonds, electrostatic interaction, etc.) under the aggregated state, this polymer film exhibited a promising acid & base‐driven multiple chirality inversion property containing record switchable chiral states (up to five while the solution showed three‐state switching) and good reversibility. The creative exploration of such a multiple chirality switching material can not only promote the application progress of current chiroptical regulation technology, but also provide a significant guidance for the design and synthesis of future smart chiroptical switching materials and devices.

Multiple Chirality Switching of a Dye-Grafted Helical Polymer Film Driven by Acid & Base.

A stimuli-responsive multiple chirality switching material, which can regulate opposed chiral absorption characteristics, has great application value in the fields of optical modulation, information storage and encryption, etc. However, due to the rareness of effective functional systems and the complexity of material structures, developing this type of material remains an insurmountable challenge. Herein, a smart polymer film with multiple chirality inversion properties was fabricated efficiently based on a newly-designed acid & base-sensitive dye-grafted helical polymer. Benefited from the cooperative effects of various weak interactions (hydrogen bonds, electrostatic interaction, etc.) under the aggregated state, this polymer film exhibited a promising acid & base-driven multiple chirality inversion property containing record switchable chiral states (up to five while the solution showed three-state switching) and good reversibility. The creative exploration of such a multiple chirality switching material can not only promote the application progress of current chiroptical regulation technology, but also provide a significant guidance for the design and synthesis of future smart chiroptical switching materials and devices.

Effect of Synthesis Condition on Degree of Deacetylation of Chitosan from Shrimp Waste for Smart Film Applications

Shrimp is an Indonesian’s export commodity with high economic value increasing every year. Usually, shrimps are exported in the form of frozen shrimp without shells, heads, tails, and entrails. It resulted in the accumulation of shrimp waste leading to the increasing environmental pollution. Shrimp waste contains high contents of chitin which can be processed to a chitosan owing several benefits. The purpose of this study is to determine the optimum condition of the synthesis of chitosan from chitin isolated by the autolysis method. The deproteination was carried out by soaking the shrimp waste in an acidic solution (pH 2 – 3) for 10 d. The demineralization process was done by reacting the deproteinated solids in a hydrochloric acid solution at pH 0 – 1 for 24 h. Parameters varied in this study time (1 – 3 h), chitin to NaOH ratio (1:10 – 1:30 (w/v)), and temperature (60 – 120℃). The higher all parameters used, the higher the obtained degree of deacetylation (DD) which is in the range of 18.35±1.13 to 48.6±0.51%. On the other hand, the obtained yield decreased from 50.66±1.98% to 47.78±0.81%. The optimum condition was obtained at a synthesis temperature of 120℃, chitin to NaOH ratio of 1:20 g/mL, and time of 3 h producing chitosan with DD of 54.25 ± 2.27%, and yield of 47.7 ± 0.65%. Chitosan synthesized using optimum conditions produced a relatively homogeneous thin film. Polyaniline was then introduced to the film to obtain a smart film prototype. This smart film was able to detect the pH changes proven by the change in its color. The smart film also could be potentially used as a “smart pack” for detecting product decay which releases ammonia gas.

Photothermal synergistic modulation of patterned VO2-Based composite films for smart windows

Vanadium dioxide (VO2) emerges as promising material for smart windows due to its ability to dynamically modulate the characteristics of near-infrared light during phase transition, accompanied by a relatively high luminous transmittance (Tlum). However, traditional VO2-based smart windows have predominantly emphasized achieving high solar modulation ability (ΔTsol), often overlooking the modulation of emissivity (ε) of long-wave infrared (LWIR). This oversight makes it challenging to achieve optimal energy-saving effects. To address this, patterned smart window composite films are designed and optimized by using Fabry-Pérot cavity to achieve dual-band coordinated regulation of sunlight and thermal radiation, which can greatly improve the energy-saving efficiency. The obtained composite film has a great low-temperature luminous transmittance (Tlum-L=50.4 %) and a high solar modulation ability (ΔTsol = 13.9 %). Meanwhile, the composite film can adaptively adjust its emissivity, with emissivity values of 0.67 and 0.18 at high and low temperatures, respectively, endowing it with excellent thermal radiation regulation capabilities. The development of patterned composite films is of great significance in the field of thermal control smart windows, which has great potential in improving the energy efficiency of buildings and enhancing resident comfort.

The application of film based on gelatin/hydroxymethyl cellulose and red beetroot betalain in smart food packaging.

Edible films containing anthocyanin and betacyanin as indicators of freshness are promising systems for food smart packaging. This research aimed to develop a smart color film for food packaging using gelatin/hydroxypropylmethyl cellulose (HPMC) and red beet betalain. In this study, edible films with different ratios of gelatin to HPMC were prepared successfully, and the ratio of 3:1 was determined as optimal samples based on water vapor permeability (WVP) and mechanical properties. Betalain with different concentrations was then added to the optimal film, and the physical and mechanical properties of the resulting films were evaluated. Also, TVB-N test to assess their ability to detect beef meat and shrimp spoilage was studied. The addition of betalain improved the solubility, WVP, mechanical properties, and 2,2-diphenyl-l-picrylhydrazyl free radical scavenging activity of the film. As a final point, the incorporation of betalain into the gelatin/HPMC films can be used to indicate the freshness of food.

An intelligent myofibrillar protein film for monitoring fish freshness by recognizing differences in anthocyanin (Lycium ruthenicum)-induced color change

A novel smart film MP/BNC/ACN for real-time monitoring of fish freshness was developed using myofibrillar protein (MP) and bacterial nanocellulose (BNC) as film raw materials and anthocyanin (Lycium ruthenicum, ACN) as an indicator. Firstly, the film containing 1 % ACN (MP/BNC/ACN1) was found to have a moderate thickness (0.44 ± 0.01 mm) and superior mechanical properties (tensile strength (TS) = 8.53 ± 0.11 MPa; elongation at break (EB) = 24.85 ± 1.38 %) by determining the physical structure. The covalent, electrostatic, and hydrogen bonding interactions between anthocyanin and the film matrix were identified and confirmed by FT-IR spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscope (SEM) analysis. A comprehensive evaluation concluded that MP/BNC/ACN1 exhibited excellent trimethylamine (TMA) sensitivity (total color difference (ΔE), ΔETMA0-1000 = 4.47–31.05; limit of detection (LOD), LOD = 1.03) and UV stability (ΔE96h = 4.16 ± 0.13). The performance of the films in assessing fish freshness was evaluated, principal component analysis (PCA) and hierarchical cluster analysis (HCA) revealed that MP/BNC/ACN1 (ΔE2-10d = 16.84–32.05) could clearly distinguish between fresh (0–2 d), sub-fresh (4–6 d), and spoiled (8–10 d) stages of fish, which corresponded to the film colors of red, light red, and gray-black. In conclusion, this study addresses the limitation that intelligent films cannot visually discern real-time freshness during fish storage and provides a promising approach for real-time fish freshness monitoring.

Utilization of torrefied date stones with synthesized TiO2 nanoparticles for promoting humidity sensing of PVA/PVP nanocomposites for smart food packaging and biomedical applications

Fabricating smart and active packaging films with affordable cost has become the first demand for serving to market needs, particularly after COVID-19 disaster, for ensuring food security. Therefore, the broader goal of this work was to improve intelligent and active packaging films having humidity-sensing and antibacterial properties for biodegradable poly vinyl alcohol (PVA)/Polyvinylidene (PVP) reinforced with torrefied date stones (DS) and lethal amounts of TiO2 nanoparticles by a solvent-casting approach. Various concentrations of TiO2 NPs (i.e. 0.05, 0.15, and 0.30 %) in presence of 10 % torrefied DS (biochar) as a fixed content were used to fabricate PVA/PVP nanocomposite films. FT-IR spectra were utilized to monitor the DS functional groups before and after torrefaction at 270 °C. The crystal structure of synthesized TiO2 NPs as well as its impact on the PVA/PVP nanocomposites were verified by X-ray diffraction (XRD). The XRD micrographs and FT-IR spectra-based biofilms showcased that the degree of crystallinity and dispersibility of filler in the blend matrix were promoted, when the nanoparticles added. This was evidenced by SEM images. Mechanical testing also manifested that a great improvement in the tensile properties were noticed, especially at 0.30 % NPs and found the tensile strength reached ∼33 MPa compared to PVA/PVP blank (∼23.70 MPa) or PVA/PVP-BC (∼18.20 MPa). The humidity sensing properties were performed over a wide span of relative humidity from (11–97 % RH) and frequency (50 Hz-10 kHz). The data manifested that 100 Hz was the optimum testing frequency. Moreover, the gotten findings from humidity-sensing tests at 100 Hz exhibited that the sensor containing 0.15 % TiO2 NPs had higher sensitivity and could be considered as a nano-sensor for smart food packaging. Furthermore, the impact of TiO2 NPs on antibacterial activity was investigated to probably use these films in active packaging with prolonged shelf-life of food products and other promising applications including biological area.

Fabricating a high-loading smart film to monitor pork freshness via adsorption of anthocyanins on simultaneously etched, anionized and bleached wood cell wall

In this paper, wood cell walls were simultaneously roughened, carboxylated, and bleached via NaOH/H2O2 treatment and roughened-poplar film (RPF) was obtained. Compared with the untreated film, the carboxyl group content increased 8 times to 1.92 mmol/g, and the pore growth rate reached 11.24%. Afterwards, a pH-indicator wood film (CTA-RPF) was prepared by self-adsorption of anthocyanins on RPF. It rapidly changed from purple to green within 7 s in 0.25 mL of ammonia at 53% RH and the initial color could restore in the air. When anthocyanins adsorption capacity reached 1.95 mg/g, only 0.36 cm2 of the film could accurately indicate the quality change of 300 g pork. Currently, CTA-RPF is the smallest smart film that can track the maximum mass of pork after comparing with other researches, therefore, promising to be used as a smart indicator label to track the freshness of pork in real market circulation.

Comparison of Physical and Functional Characteristics of Biodegradable Smart Films Embedded with Betacyanin-Rich Extracts from Different Sources

Comparison of Physical and Functional Characteristics of Biodegradable Smart Films Embedded with Betacyanin-Rich Extracts from Different Sources

MXene-powered flexible smart windows for sustained bending performance

Ti3C2Tx MXene is renowned for its high conductivity and flexibility, making it ideal for various applications. This study focuses on developing flexible and durable Polymer-dispersed liquid crystal (PDLC) based smart windows using Ti3C2Tx MXene-coated PET films, demonstrating sustained bending performance over 10,000 cycles. The fabrication process involved spin-coating of MXene dispersion (average flakes size ∼400 nm) on PET film to fabricate flexible transparent conductive electrodes (TCE) having a sheet resistance (Rs) of ∼550 Ω.sq.−1 and a transmittance of ∼80 % (at 550 nm). PDLC mixture containing liquid crystals and NOA65 monomer were sandwiched within MXene electrodes to prepare PDLC-based smart windows having a transmittance of ∼75 %. UV-cured polymer contributes to mechanical stability, while the Ti3C2Tx MXene electrodes impart electrical conductivity to the smart windows. The MXene electrodes demonstrate remarkable flexibility as evidenced by a minimal change in resistance, with a strain of 0.8 % resulting in a 0.7 % change in relative resistance (∆R/Ro) at a bending radius of ∼7.5 mm. The durability of flexible smart windows was investigated till 10000 bending cycles (bending radius of ∼9.5 mm). After sustained bending the smart films maintain ON-state transmittance in the 70–75 % range. These smart windows exhibit a variation of <5 % in ΔT (difference between OFF and ON-state transmittance) and the contrast ratio after 10000 bending cycles. These smart windows feature rapid switching time (ON/OFF) along with low power consumption of ∼8 Wm−2.

Active and smart biomass film with curcumin Pickering emulsion stabilized by chitosan-adsorbed laurate esterified starch for meat freshness monitoring

The multifunctional active smart biomass film was prepared by incorporating chitosan-adsorbed laurate esterified starch curcumin Pickering emulsion into the starch film matrix, with nano-cellulose serving as reinforcing agents. The mechanical and functional properties of the film were studied, and the film was used to monitor the freshness of pork. The results demonstrated a relatively uniform distribution of curcumin and Pickering emulsion droplets within the film matrix. Furthermore, the thermal stability was minimally impacted by the introduction of curcumin Pickering emulsion, while the tensile strength and tensile strain of the film were increased, and both its hydrophobicity and antioxidant properties were improved. The free radical scavenging rate reached 56.01 %, with sustained high antioxidant capacity even after 8 days. Additionally, the presence of curcumin provided the film with pH indicating ability and delayed pork spoilage. Therefore, this work provides an attractive strategy for constructing green, active, and smart biomass packaging films for meat packaging applications.

Novel pullulan-sodium alginate film incorporated with anthocyanin-loaded casein-carboxy methyl cellulose nanocomplex for real-time fish and shrimp freshness monitoring

This study fabricated novel smart colorimetric film from pullulan (P) and sodium alginate (SA) incorporated with anthocyanin (ACNs) loaded casein carboxymethylcellulose (CAS-CMC-ACNs) nanocomplex for the freshness monitoring of the fish and shrimp. The ACNs loaded nanocomplex exhibited large particle size (176.902 ± 4.641 nm) than CAS-CMC (155.454 ± 4.152 nm) nanocomplex without ACNs, and can be loaded in P/SA film with uniform distribution. The P/SA film incorporated with CAS-CMC-ACNs nanocomplex had a more compact structure, improved barrier properties, mechanical strength, and thermal stability than P/SA film incorporated with free ACNs, which could be attributed to hydrogen bonding among the components in the film matrix, as confirmed by SEM micrographs and FT-IR. Intriguingly, the composite film exhibited antibacterial effect against gram-negative bacteria E. coli (Escherichia coli) and gram-positive bacteria S. aureus (Staphylococcus aureus) with inhibition zone of 7 ± 0.283 mm and 8.6 ± 0.141 mm, and antioxidant effect. The composite film demonstrated a visible response to CO2 and pH buffer. Furthermore, the composite smart film demonstrated the potential to monitor the freshness of fish and shrimp stored at 25 °C for 24 h via a visual color change from pink to dark grey. The findings revealed that the fabricated film is an effective tool for evaluating the freshness of fish and shrimp.

Smart films based on semiconductor heterojunctions of mechanoluminescent sulfide and sulfur oxide for stress sensing and anti-counterfeiting applications

Mechanoluminescent (ML) materials offer significant potential for remote stress sensing and distribution. However, creating highly sensitive and responsive ML materials remains a challenge. In this study, mechanoluminescent semiconductor materials have been successfully prepared as Mn2+ doped ZnS-SrZnOS heterojunction composites. These materials exhibit high-resolution stress distribution visualization and rapid response, captured via camera recording. Notably, they possess a low stress triggering threshold, reaching the KPa level, and respond within milliseconds. Furthermore, it was found that by adjusting the doping concentration of Mn2+ within the heterojunction, the material utilizes its bimodal emission capability to manipulate the fluorescence shift and achieve optical anti-counterfeiting. The synthesis of smart films by combining the material with polydimethylsiloxane matrix had enabled the achievement of collision detection, information hiding and optical anti-counterfeiting. These results suggest that the prepared smart films have wide range of optical sensing applications.

Indicative bacterial cellulose films incorporated with curcumin-embedded Pickering emulsions: Preparation, antibacterial performance, and mechanism

Biodegradable, sustainable, and multifunctional intelligent food packaging has attracted extensive attention due to the concerns about the environmental pollution, the health hazard, and the food safety of plastic packaging. Herein, a multifunctional bacterial cellulose (BC)-based film (termed BC-PE-Cur) was fabricated for intelligent food packaging. The film was simply prepared by vacuum filtration and compression of a mixture of the BC and the curcumin (Cur)-embedded Pickering emulsion (PE) stabilized with the natural protein-polysaccharide hybrid nanoparticles (PPH NPs). The Pickering emulsion droplets containing Cur were uniformly distributed within the film and adhered to the film surface, resulting in a uniform dispersion of Cur in the film, and a thicker, rougher film with a laminated pore structure. The BC-PE-Cur film showed excellent antibacterial, antioxidant, UV-shielding, water vapor barrier, and mechanical properties. BC-PE-Cur film can extend the shelf life of basa fish by delaying the lipid peroxidation and inhibiting the growth of spoilage microorganisms. Moreover, during the storage of basa fish, BC-PE-Cur films underwent significant color change due to the production of alkaline substances, which could indicate the freshness of basa fish. This study provides an attractive strategy to construct multifunctional smart bio-based composite films containing non-water-soluble active ingredients for food packaging and freshness monitoring.

Potato oxidized hydroxypropyl starch/pectin-based indicator film with Clitoria ternatea anthocyanin and silver nanoparticles for monitoring chilled beef freshness

Potato oxidized hydroxypropyl starch (POHS)/pectin (P) functional and smart beef freshness indicator films were prepared using butterfly pea (Clitoria ternatea) anthocyanin (BA) and silver nanoparticles (AgNPs). BA exhibited significant pH-responsive color changes. BA and AgNPs were evenly distributed within a polymer matrix to create a compatible film with POHS/P. The films containing BA and AgNPs had good UV resistance and maintained strong mechanical strength, barrier properties, and color stability. The color of the indicator film changed from purple to green when exposed to ammonia, with the 1 % POHS/P/BA/AgNPs film showing the most sensitive response. The films also demonstrated strong antibacterial and antioxidant properties. The freshness of beef was monitored using 1 % POHS/P/BA/AgNPs films and was identified as sub-fresh and spoiled on days 4 and 7, respectively. The relationship between the color change of the indicator label and the freshness of chilled beef was established: purple for fresh meat, blue for less fresh meat, and green for spoiled meat. Thus, the new POHS/P/BA/AgNPs film can serve as a smart packaging material to indicate food freshness and extend shelf life. These results suggest that POHS/P/BA/AgNPs films have significant potential as an active and smart food packaging material.

Development and characterization of cellulose‐based smart films extracted from coconut waste

AbstractThe increasing demands for safe and quality packaged food have diverted all the intentions toward the enhancement of hazard detection and quantification techniques. The integration of smart functions with the novel biomaterials‐based packaging provides an effective approach to deal with the uplifting concerns of food safety and environmental pollution. In the current study, firstly the cellulose was extracted from coconut waste, then it was subjected to prepare biodegradable films and lastly the films were incorporated with curcumin or quercetin dihydrate. The films were characterized for their mechanical, barrier and smart properties. The incorporation of curcumin or quercetin dihydrate improved the physicochemical properties of the cellulose films, including strength, elongation at break (EAB), water vapor permeability (WVP), biodegradability, antioxidant and antimicrobial activity. However, the moisture content and water solubility decreased. The scanning electron microscopy (SEM) images depicted the rough surface of curcumin incorporated smart films which represents successful application of curcumin, while cracks and pits were observed for the films with the higher concentration of quercetin dihydrate. All the smart films showed effective responses against pH ranging from 2 to 14.