Controlling the microstructure of poly(vinylidene-fluoride) (PVDF) thin films for microelectronics

Abstract

PVDF thin films prepared under standard processing conditions have a cloudy appearance and are notoriously rough, which prevent microelectronic and photonic applications. On the other hand, high optical quality, smooth films can be prepared either at low relative humidity or at high substrate temperature. Here we systematically investigate the morphology of PVDF thin films by varying the processing conditions. Films are characterized by SEM and AFM and by measurements of clarity, haze and absorption. We show that the cloudy appearance is due to vapor-induced phase separation (VIPS) as is well-documented for the formation of PVDF membranes. Formation of opaque thin films is a general problem of any ternary polymer/solvent/non-solvent system where a high boiling point solvent is used that is fully miscible with a non-solvent, here water from the ambient.

Improving Liquid Entry Pressure of Polyvinylidene Fluoride (PVDF) Membranes by Exploiting the Role of Fabrication Parameters in Vapor-Induced Phase Separation VIPS and Non-Solvent-Induced Phase Separation (NIPS) Processes

“…A polymer-rich phase with composition S is marked in Figure 2 as well as a polymer-lean phase with composition L. Point L represents the composition of the voids or pores of the membrane which contain water which eventually evaporate during the drying stage. At the other extreme, when a VIPS process is applied without the final coagulation bath step, delayed demixing leads the compositional pathway to follow path A ( Figure 2) [21]. In this case, the rate of non-solvent intrusion into the casted polymer film is much slower than the rate of solvent extrusion.…”

“…As the composition crosses the crystallization line, the polymer solution solidifies, forming crystal nuclei and eventually forming a membrane with crystalline structures (evidence of this is discussed later, Figure 6). Compositional paths B-F and C-E ( Figure 2) represent a combination of a complete NIPS (pathway D) and a complete VIPS (pathway A) process [21,22]. As the RH increases, the compositional path moves from pathway A towards D, with B-F and C-E representing two RH cases with B-F having a lower RH than C-E. As the RH increases, the chemical potential difference between the polymer solution and the atmosphere surrounding it increases as well, leading to a higher rate of absorption of water (as can be seen later in Figure 8).…”

“…Pathway C is similar to B but with an even higher RH and a different exposure time. Here, the membrane is immersed in the coagulation bath after it crosses the spinodal line [21] moving from path C to E. towards D, with B-F and C-E representing two RH cases with B-F having a lower RH than C-E. As the RH increases, the chemical potential difference between the polymer solution and the atmosphere surrounding it increases as well, leading to a higher rate of absorption of water (as can be seen later in Figure 8). Pathway B-F starts in a similar way to path A, but with a higher RH.…”

Coaxial Electrospun Cellulose-Core Fluoropolymer-Shell Fibrous Membrane from Recycled Cigarette Filter as Separator for High Performance Lithium-Ion Battery

“…Therefore, more polar and higher ionic conductive polyvinylidene fluoride (PVDF) and its copolymer, poly(vinylidene fluoride-cohexafluoropropylene) (PVDF-HFP), have received special attention as promising host polymers for separators in LIBs. 11−13 However, PVDF and PVDF-HFP separators also have their disadvantages, such as the inferior thermal stability due to their low softening or melting behavior, 14,15 making it difficult to serve the critical function of electronic isolation between cathode and anode in large-sized batteries at elevated temperatures or under vigorous conditions. A few studies have pointed out that poor liquid electrolyte retention due to their intrinsically hydrophobic character would restrict applications in high performance lithium-ion batteries.…”

Thin film thermistor with positive temperature coefficient of resistance based on phase separated blends of ferroelectric and semiconducting polymers

“…Substrate temperature was chosen as 80 C to minimize the surface roughness. 27,28 Subsequently, films were annealed at 140 C for 2 h in vacuum to enhance the crystallinity of P(VDF-TrFE) and, hence, to enhance its ferroelectric properties. 29 Ferroelectric hysteresis loops of comprising capacitors are presented in Fig.…”