Pressure-sensitive Adhesives Research Articles

Ginger oil-loaded transdermal adhesive patch treats post-traumatic stress disorder

ObjectiveTo find a viable alternative to reduce the number of doses required for the patients with post-traumatic stress disorder (PTSD), and to improve efficacy and patient compliance. MethodsIn this study, we used ginger oil, a phytochemical with potential therapeutic properties, to prepare ginger oil patches. High-performance liquid chromatography (HPLC) was used to quantify the main active component of ginger oil, 6-gingerol. Transdermal absorption experiments were conducted to optimize the various pressure-sensitive adhesives and permeation enhancers, including their type and concentration. Subsequently, the ginger oil patches were optimized and subjected to content determination and property evaluations. A PTSD mouse model was established using the foot-shock method. The therapeutic effect of ginger oil patches on PTSD was assessed through pathological sections, behavioral tests, and the evaluation of biomarkers such as tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), brain-derived neurotrophic factor (BDNF), and melatonin (MT). ResultsThe results demonstrated that ginger oil patches exerted therapeutic effects against PTSD by inhibiting inflammatory responses and modulating MT and BDNF levels. Pharmacokinetic experiments revealed that ginger oil patches maintained a stable blood drug concentration for at least one day, addressing the rapid metabolism drawback of 6-gingerol and enhancing its therapeutic efficacy. ConclusionsGinger oil can be prepared as a transdermal drug patch that meets these requirements, and the bioavailability of the prepared patch is better than that of oral administration. It can improve PTSD with good patient compliance and ease of administration. Therefore, it is a promising therapeutic formulation for the treatment of PTSD.

UV‐photopolymerized acrylic pressure‐sensitive adhesives with semi‐interpenetration structure: Effect of plasticizer structures on adhesion properties

AbstractAcrylic pressure‐sensitive adhesives (PSAs) were synthesized using a solvent‐free ultraviolet‐induced polymerization method. The monomers n‐(isobutoxymethyl) acrylamide, 2‐ethylhexyl acrylate, 2‐hydroxyethyl acrylate, and methyl methacrylate and an initiator, hydroxy dimethyl acetophenone, were used to prepare acrylic copolymers as prepolymers. A multifunctional monomer, trimethylolpropane triacrylate, was added to form a semi‐interpenetrating network, leading to an increase in the modulus and elasticity of the prepolymer. This decreased the peel strength, which is suitable for temporary protective films. Rheological data from small‐amplitude oscillatory shear measurements also revealed consistent results suitable for removable PSAs. The plasticizers, such as dioctyl phthalate and dioctyl terephthalate, possessing favorable interactions with the main resins were found to exhibit transparency, clear debonding, and ultralow release, which are essential features for temporary protective films.

Preparation and characterization of long carbon chain based polyacrylate latexes and their pressure sensitive adhesive application

Aqueous emulsion homo- and co-polymerization of lauryl methacrylate (LMA), a strong hydrophobic monomer with long carbon chain, is quite challenging. In this study, a long carbon chain emulsifier N-390 was used as the primary emulsifier to facilitate the emulsion copolymerization of LMA with other acrylate monomers through the mutual hydrophobic interaction between N-390 and LMA, and ultimately polyacrylate latex pressure sensitive adhesives modified by LMA via pre-emulsified semi-continuous seeded emulsion polymerization process were synthesized. The effects of LMA on the resulting latex and PSA properties was comprehensively examined. Both FTIR and 1H NMR spectra indicated that LMA has been successfully introduced into copolymer chain with the aid of long carbon chain emulsifier N-390. The results also showed that the introduction of LMA will contribute to decrease in particle size and zeta potential, while increase viscosity and gel content of the acrylate PSA latex. Moreover, as the LMA content increased, the latex PSA films demonstrated gradual improvements in both water resistance and thermal stability. Finally, for the long carbon chains adhesive film, the shear strength was improved greatly while at the sacrifice of loop tack and peel strength, when compared to counterparts without LMA.

Bulk Free Radical Terpolymerization of Butyl Acrylate, 2-Methylene-1,3-Dioxepane and Vinyl Acetate: Terpolymer Reactivity Ratio Estimation.

This investigation introduces the first estimation of ternary reactivity ratios for a butyl acrylate (BA), 2-methylene-1,3-dioxepane (MDO), and vinyl acetate (VAc) system at 50 °C, with an aim to develop biodegradable pressure-sensitive adhesives (PSAs). In this study, we applied the error-in-variables model (EVM) to estimate reactivity ratios. The ternary reactivity ratios were found to be r12 = 0.417, r21 = 0.071, r13 = 4.459, r31 = 0.198, r23 = 0.260, and r32 = 55.339 (BA/MDO/VAc 1/2/3), contrasting with their binary counterparts, which are significantly different, indicating the critical need for ternary system analysis to accurately model multicomponent polymerization systems. Through the application of a recast Alfrey-Goldfinger model, this investigation predicts the terpolymer's instantaneous and cumulative compositions at various conversion levels, based on the ternary reactivity ratios. These predictions not only provide crucial insights into the incorporation of MDO across different initial feed compositions but also offer estimates of the final terpolymer compositions and distributions, underscoring their potential in designing compostable or degradable polymers.

Polymeric surfactants with high acid values for emulsion type pressure-sensitive adhesives

Low molecular weight polymers with hydrophobic-carboxyl groups have been usually used as anionic surfactants in emulsion polymerization for coatings. However, such polymeric surfactants usually have low acid values below 200, because it is difficult to make high acid-value polymeric surfactants using a normal batch reactor. In this work, we polymerized high acid value polymeric surfactant having high acid values successfully up to 380 using CSTR (continuous stirring tank reactor). The synthesized polymeric surfactant was a random copolymer of P(BA-AA) and we applied them as anionic surfactants in making emulsion-type acrylic PSAs (Pressure-Sensitive Adhesives) to investigate the effects of high acid values on the adhesive properties. This CSTR can effectively control the composition and molecular weight of polymeric surfactants through varying monomer ratios, retention time, and initiator concentrations. The surface tension analysis and emulsion stability test indicated that the synthesized polymeric surfactants exhibited a similar levels of critical micelle concentration (CMC) and emulsion stability with other conventional anionic surfactants. Also, the adhesion property analysis showed that the PSA used high acid value polymeric surfactant resulting in superior adhesive properties and heat resistance than the PSAs used low acid value polymeric surfactant or conventional low molecular weight surfactant. It was very notable that polymeric surfactants having unusually high acid values above 300 because of their high contents of carboxylic acid groups could result in superior adhesive properties and heat resistance.

Ring‐Opening Copolymerization of Biorenewable δ‐Caprolactone with trans‐Hexahydro‐(4,5)‐benzofuranone toward Closed‐Loop Recyclable Copolyesters and Their Application as Pressure‐Sensitive Adhesives†

Comprehensive SummaryCopolymerization as an efficient strategy can provide an opportunity to create new closed‐loop recyclable polymeric materials with tailored properties that are generally inaccessible to the individual homopolymers. In this contribution, the bulk ring‐opening copolymerization of bio‐renewable δ‐caprolactone and trans‐hexahydro‐(4,5)‐benzofuranone was achieved to produce closed‐loop recyclable copolyesters by using an organobase/urea binary catalyst at room temperature. The obtained copolyesters exhibited composition‐dependent thermal properties. Remarkably, the obtained copolyesters were able to depolymerize back to recover the corresponding monomers under mild conditions. The copolyesters with suitable compositions can be directly used as pressure‐sensitive adhesives (PSAs) that possessed comparable peel strength with the commercially available PSA scotch tapes. When the copolyesters were mixed with plasticizers, the as‐prepared PSAs exhibited desirable adhesive failure and can be used as removable post‐it note.

Analytical model for static and cyclic creep behavior of pressure-sensitive adhesives

The increasing interest in adhesives, such as pressure-sensitive adhesives (PSAs), is often held back by uncertainties regarding their long-term behavior, which includes creep behavior. However, little information exists in the literature regarding creep behavior of PSAs. In this paper, a unified phenomenological creep model for PSAs is applied in SLJs for static and cyclic creep, seeking to develop a tool to predict creep behavior of PSAs. The model was validated by comparing the predicted creep curves with experimental data. It captured the three creep phases and predicted the creep curves for different stresses and temperatures, which is uncommon in literature.

Biodegradable Polyurethane Pressure-Sensitive Adhesives Using Biobased Polyols with Distinct Intrinsic Properties

Biodegradable Polyurethane Pressure-Sensitive Adhesives Using Biobased Polyols with Distinct Intrinsic Properties

The Effect of Cellulose Nanocrystal Reassembly on Latex-Based Pressure-Sensitive Adhesive Performance.

Different cellulose nanocrystal (CNC) forms (dried vs never-dried) can lead to different degrees of CNC reassembly, the formation of nanofibril-like structures, in nanocomposite latex-based pressure-sensitive adhesive (PSA) formulations. CNC reassembly is also affected by CNC sonication and loading as well as the protocol used for CNC addition to the polymerization. In this study, carboxylated CNCs (cCNCs) were incorporated into a seeded, semibatch, 2-ethylhexyl acrylate/methyl methacrylate/styrene emulsion polymerization and cast as pressure-sensitive adhesive (PSA) films. The addition of CNCs led to a simultaneous increase in tack strength, peel strength, and shear adhesion, avoiding the typical trade-off between the adhesive and cohesive strength. Increased CNC reassembly resulted from the use of dried, redispersed, and sonicated cCNCs, along with increased cCNC loading and addition of the cCNCs at the seed stage of the polymerization. The increased degree of CNC reassembly was shown to significantly increase the shear adhesion by enhancing the elastic modulus of the PSA films.

A semi-interpenetrating network acrylic pressure-sensitive adhesive for efficient transdermal application with high cohesion and adhesion

The application of pressure-sensitive adhesives (PSAs) in transdermal drug delivery systems (TDDSs) is limited. Insufficient cohesion in TDDS can lead to cold flow, patch displacement, dose inaccuracies, and the ‘dark ring’ phenomenon. To address these issues, we developed a semi-interpenetrating network (semi-IPN) PSA using a 2-hydroxyethylacrylate-modified acrylic copolymer as the linear polymer and poly[tri(propylene glycol) diacrylate] as the cross-linked network. Semi-IPN PSAs have better mechanical properties compared to traditional PSAs. The cohesion of the semi-IPN PSA was 31 times and 1.6 times that of commercially available DURO-TAK®87-2287 and DURO-TAK® 87–4098, respectively, and the cold flow of the semi-IPN PSA was significantly reduced. Furthermore, the semi-IPN PSA adhered to the human forearm for longer time and did not exhibit the ‘dark ring’ phenomenon after removal. When loaded with flurbiprofen, the semi-IPN PSA was found to maintain high levels of drug release and skin permeation amount, and flurbiprofen loading did not affect its superior cohesive performance. In conclusion, the innovative application of the semi-IPN PSA for TDDS showed excellent mechanical properties, effective adhesion to the skin without irritation, and highly effective drug release. These findings indicate that the use of the semi-IPN is both simple and highly effective for TDDS.

Mechanical simulation and debonding risk analysis of OLED panels with optically clear adhesives

This paper presents a mechanical simulation model and analysis method for OLED panels. The functional layers within the panel are bonded using optically clear adhesives (OCAs), which are pressure-sensitive adhesives (PSAs), resulting in a soft interface bonding problem. It was discovered that the normal tensile debonding strength of OCAs was significantly lower than the shear debonding strength. To address this issue, a three-layer structure simulation model of “hard + soft + hard” is established, which allows for analyzing the screen folding problem of any radius. Additionally, a suitable element mesh generation strategy for multi-layer structure screens is proposed. A debonding risk index based on pressure is introduced by comparing the interlaminar normal and maximum principal stress. The influence of thickness, bending radius, and Young’s modulus on longitudinal stress and debonding risk index is examined. It is observed that the influence of thickness and Young’s modulus on debonding risk is non-monotonic, indicating the presence of an optimal solution. The high debonding risk area is located at the beginning of the folding mechanism and screen bonding. The proposed debonding risk index is not only applicable to OCAs but also to all PSA with similar structures.

A strong, silk protein-inspired tissue adhesive with an enhanced drug release mechanism for transdermal drug delivery

In transdermal drug delivery system (TDDS) patches, achieving prolonged adhesion, high drug loading, and rapid drug release simultaneously presented a significant challenge. In this study, a PHT-SP-Cu2+ adhesive was synthesized using polyethylene glycol (PEG), hexamethylene diisocyanate (HDI), trimethylolpropane (TMP), and silk protein (SP) as functional monomers which were combined with Cu2+ to improve the adhesion, drug loading, and drug release of the patch. The structure of the adhesion chains and the formation of Cu2+-p-π conjugated network in PHT-SP-Cu2+ were characterized and elucidated using different characterization methods including FT-IR, 13C NMR, XPS, SEM imaging and thermodynamic evaluation. The formulation of pressure-sensitive adhesive (PSA) was optimized through comprehensive research on adhesion, mechanics, rheology, and surface energy. The formulation of 3 wt.% SP and 3 wt.% Cu2+ provided superior adhesion properties compared to commercial standards. Subsequently, the peel strength of PHT-SP-Cu2+ was 7.6 times higher than that of the commercially available adhesive DURO-TAK® 87–4098 in the porcine skin peel test. The adhesion test on human skin confirmed that PHT-SP-Cu2+ could adhere to the human body for more than six days. Moreover, the drug loading, in vitro release test and skin permeation test were investigated using ketoprofen as a model drug, and the results showed that PHT-SP-Cu2+ had the efficacy of improving drug compatibility, promoting drug release and enhancing skin permeation as a TDDS. Among them, the drug loading of PHT-SP-Cu2+ was increased by 6.25-fold compared with PHT, and in the in vivo pharmacokinetic analysis, the AUC was similarly increased by 19.22-fold. The mechanism of α-helix facilitated drug release was demonstrated by Flori-Hawkins interaction parameters, molecular dynamics simulations and FT-IR. Biosafety evaluations highlighted the superior skin cytocompatibility and safety of PHT-SP-Cu2+ for transdermal applications. These results would contribute to the development of TDDS patch adhesives with outstanding adhesion, drug loading and release efficiency. Statement of significanceA new adhesive, PHT-SP-Cu2+, was created for transdermal drug delivery patches. Polyethylene glycol, hexamethylene diisocyanate, trimethylolpropane, silk protein, and Cu2+ were used in synthesis. Characterization techniques confirmed the structure and Cu2+-p-π conjugated networks. Optimal formulation included 3 wt.% SP and 3 wt.% Cu2+, exhibiting superior adhesion. PHT-SP-Cu2+ showed 7.6 times higher peel strength than DURO-TAK® 87–4098 on porcine skin and adhered to human skin for over six days. It demonstrated a 6.25-fold increase in drug loading compared to PHT, with 19.22-fold higher AUC in vivo studies. α-helix facilitated drug release, proven by various analyses. PHT-SP-Cu2+ showed excellent cytocompatibility and safety for transdermal applications. This study contributes to developing efficient TDDS patches.

Fabrication of core-shell polyacrylate latex pressure sensitive adhesives modified by fluorinated monomer and film properties

In this work, a series of fluorinated core-shell polyacrylate latex pressure sensitive adhesives (PSAs) were successfully synthesized through monomer-starved seeded semi-continuous emulsion polymerization. Specifically, (meth)acrylate monomers were employed as the main materials, with dodecafluoroheptyl methacrylate (DFMA) were used as modified monomer. The impact of fluorine monomer DFMA on the resulting core-shell latex and PSA properties was thoroughly examined. FTIR analysis confirmed the successful incorporation of DFMA into the latex copolymer through emulsion polymerization. TEM images illustrated that the morphology of latex particles exhibit a distinct core-shell structure. The results also showed that with the addition of DFMA, the water absorption and water whitening of the latex films decreased, while the water contact angle and thermal stability are improved. Interestingly, the latex films with DFMA added to the shell phase exhibit a larger WCA value when compared to those with DFMA in the core phase, further confirmed by XPS results. Finally, the adhesive properties of the fluorinated core-shell acrylate PSA were evaluated. The results of shear strength and gel content demonstrate that the prepared PSA exhibits excellent cohesive properties. Thus, this work could present a feasible strategy for optimizing the comprehensive properties of acrylate latex PSAs.

Crosslinkable latex-based acrylic adhesives containing functionalized cellulose nanocrystals (fCNCs)

In this study, crosslinkable acrylic adhesives with functionalized cellulose nanocrystal (fCNCs) were prepared via in situ emulsion polymerization at 80 °C for 3h. The neat acrylic pressure sensitive adhesives (PSAs) without any nanoparticles were prepared using butyl acrylate (BA), 65 wt%, and methyl methacrylate (MMA), 35 wt%, and various amounts of 2-hydroxyethyl methacrylate (HEMA), 1, 3, 5, 7 wt% based on total BA and MMA monomers. For preparing fCNCs reinforced adhesives, the cellulose nanocrystals (CNCs) were functionalized using various concentrations of 3-methacryloxypropyl trimethoxy silane (MPS), 5, 20, 40 mM. The cellulose nanocrystals (CNCs), functionalized cellulose nanocrystals (fCNCs), and the prepared adhesives were characterized by Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), thermal gravimetric analysis (TGA), and differential scanning calorimetry (DSC). The Adhesion performance of the adhesives was evaluated by lap shear and 180° peel tests. The results showed that increasing the HEMA content as crosslinking agent in the adhesive structure, enhanced its gel content, glass transition temperature (Tg), thermal stability, and adhesive performance, i.e. lap shear and peel strength. Finally, the adhesive containing 5 wt% HEMA was selected as the appropriate sample. Thereafter, the adhesives containing 5 wt% HEMA were synthesized in the presence of various amounts of fCNCs, i.e. 0.5, 1, 1.5 wt%. The Adhesion performance of the neat and reinforced adhesives indicated that increasing the fCNCs to the adhesive enhanced thermal stability, gel content, lap shear and peel strength. Additionally, the fCNCs prepared using higher concentration of MPS (40 mM) was more effective on the adhesion performance than the fCNCs prepared with the lower MPS contents, 5, 20 mM. The results showed that the adhesives prepared using 1 wt% and 1.5 wt% of fCNC40 (containing 40 mM MPS) exhibited better adhesion performance.

Amphiphilic hot-melt pressure sensitive adhesives for transdermal administration made from low melt-processing temperature OSISO copolymers

Herein, an anionic polymerization method was employed to synthesize a series of amphiphilic poly(ethylene oxide-b-styrene-b-isoprene-b-styrene-b-ethylene oxide) penta-block copolymers (OSISO). Their molecular structure and properties were comprehensively characterized using GPC,1H-NMR, thermodynamic rheological testing and water contact angle test. Notably, the hydrophilic characteristics exhibited a proportional increase with the rise in poly(ethylene oxide) (PEO) content, ranging from 1.3 to 12.6 wt%. The polystyrene blocks with low number-average molecular weight (2000–3500) reduced the copolymer melt viscosity, surpassing a tenfold decrease than the control sample within the temperature range of 50–150 °C. Resultantly, this series of OSISO copolymers could be used to develop amphiphilic hot-melt pressure-sensitive adhesives (HMPSAs) by low temperature hot-melt processing method (<120 °C). HMPSAs loaded with 2 wt% of geniposide, prepared by an optimized composition formula of OSISO copolymers, tackifiers, and plasticizers (in a ratio of 5:5:2), displayed excellent in vitro drug release performance. Additionally, these adhesives presented impressive 180° peeling strength (0.05–0.14 kN/m) without residues left on the substrate in the 180° peeling tests. The incorporation of PEO block significantly enhanced both the adhesive properties and accumulative drug release. Geniposide showed a burst release behavior with a moderate accumulative drug release (15–30 wt%), attributed to the PEO phase without crystallization behavior of long PEO chains.

Self-Cross-Linking Latex Pressure-Sensitive Adhesives: Preparation and Investigation on Adhesion, Linear Viscoelastic, and Nonlinear Large-Strain Properties

Self-Cross-Linking Latex Pressure-Sensitive Adhesives: Preparation and Investigation on Adhesion, Linear Viscoelastic, and Nonlinear Large-Strain Properties

Rigid Solvent-Gels in Paper Conservation: A New Approach to Sticky Problems

ABSTRACT Pressure-sensitive adhesives (PSA) present in pressure-sensitive tape or self-adhesive labels applied on paper pose substantial problems for the long-term conservation of the substrate because they degrade upon ageing, leaving embedded stains. This paper presents the development of a method to prepare agar-based solvent-gels with high organic solvent, and low water content. The objective is to provide conservators with a versatile, cheap, and easy solution to make solvent-gels for PSA removal, to be implemented as sole treatment or included in a multi-step treatment protocol. The treatment method proposed in the case-study aims at removing aged, rubber-based adhesive residues from the printed paper cover of a book. It includes the use of silicone-based solvent cyclomethicone D5 as a treatment-aid applied just before the application of the solvent-gel. The efficiency of D5 to prevent the formation of stains and tide-lines during local gel treatment is demonstrated, and potential side-effects are also pointed out.

Experimental approach for measuring the peeling strength of a sheet bonded on a curved adherend with pressure sensitive adhesive and predicting the peeling resistance by finite element analysis

ABSTRACT To evaluate the peel resistance of a device wherein a polyimide (PI) sheet is bonded to a curved surface with a pressure-sensitive adhesive (PSA) experimentally and analytically, we applied a mechanical simulation considering the viscoelasticity of the pressure-sensitive adhesive (PSA) and the fracture energy of the bonding interface. The mechanical behavior against the local load applied on the PI sheet surface was evaluated using this simulation. To verify the accuracy of this simulation, we fabricated a local load tester that could apply a load to a local area of 8 mm in diameter and compared the mechanical behavior with the simulation results. Dynamic mechanical analysis of the PSA with a film thickness of 19 μm was performed using the nanoindentation technique. The generalized Maxwell model parameters were estimated by fitting the relaxation elastic modulus E(t) to conduct a mechanical simulation. For the double cantilever beam test to derive the interfacial fracture energy, soft PI sheets were reinforced with Al substrates. As a result of these analyses, it was confirmed that the relationship between the displacement and load obtained by this simulation agrees well with the actual local load test. This technique is useful for predicting the bonding strength of complex-shaped devices fabricated using soft adherends and adhesives.

Silanization as a strategy to design polyurethane-acrylic hybrid pressure-sensitive adhesives

Pressure-sensitive adhesives (PSAs) are a critical class of adhesives used in numerous applications. Acrylic copolymers and polyurethanes are two main categories of polymers that PSAs are made from. However, to take advantage of unique properties of both of them, polyurethane-acrylic hybrid PSAs have been proposed. To date, for synthesis of these hybrid PSAs, there should have been an acrylic comonomer containing a specific functional group to be able to react with the isocyanate group. This research was conducted to eliminate the need for such an acrylic comonomer with a specific functional group through silanization. For this purpose, firstly, a silanized polyurethane (SPU) was synthesized through silanization of a polyol. Subsequently, copolymerization of two acrylic comonomers was performed in the absence or presence of SPU. In the next step, prior to adding the acrylic comonomers to the SPU, silane was added to SPU to enable higher grafting. The PSA containing 0.04 wt % of silane showed a peel force, static shear strength, and tack of 1.6, 1.4, and 2.9 times those of the acrylic PSA on stainless steel, respectively. With this proposed silanization strategy, it is possible to design a wide variety of polyurethane-acrylic hybrid polymers.

Synthesis of Novel (Meth)acrylates with Variable Hydrogen Bond Interaction and Their Application in a Clear Viscoelastic Film.

Clear viscoelastic films (CVFs) have many applications in the display industry. Acrylic monomers containing a hydrogen bond (H-monomer) are often used in the preparation of CVF to increase the cohesion and form favorable interactions with the display substrate. Common H-monomers face a counterbalance between the glass transition temperature (Tg) and the hydrogen-bonding association constant (Ka). Strong hydrogen bonding often leads to a high Tg and high modulus, which are unfavorable in certain applications such as foldable display. To solve these problems, four types of hydrogen-bonding (meth)acrylic monomers (carbamate acrylate, carbamate methacrylate, urea acrylate, and urea methacrylate) with different Ka and Tg were readily synthesized. Among them, urea acrylates displayed the highest Ka while still maintaining moderate Tg. These H-monomers were copolymerized with 2-ethylhexyl acrylate (EHA) and cross-linked to obtain a series of copolymers (H-copolymers) as pressure-sensitive adhesives. After the characterization of rheology, optics, and peel adhesion, urea-acrylic H-copolymers showed the best overall performance by combining great optical property (>98% in transmittance, < 1% in haze) and mechanical performance (8-12 N/25 mm in peel adhesion, 84-92% in creep recovery). This work provides a new path to prepare acrylic CVF for flexible display application.