Inhibition of Heterogeneous Ice Nucleation by Bioinspired Coatings of

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Inhibition of Heterogeneous Ice Nucleation by Bioinspired Coatings of Polyampholytes Zhiyuan He, Liuchun Zheng, Zhenqi Liu, Shenglin Jin, Chuncheng Li, and Jianjun Wang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b10014 • Publication Date (Web): 16 Aug 2017 Downloaded from http://pubs.acs.org on August 16, 2017

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ACS Applied Materials & Interfaces

Inhibition of Heterogeneous Ice Nucleation by Bioinspired Coatings of Polyampholytes Zhiyuan He, Liuchun Zheng, Zhenqi Liu, Shenglin Jin, Chuncheng Li* and Jianjun Wang* Zhiyuan He, Zhenqi Liu, Shenglin Jin, Jianjun Wang* Key Laboratory of Green Printing, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100190, China University of Chinese Academy of Sciences, Beijing, 100049, P. R. China Liuchun Zheng, Chuncheng Li* Key Laboratory of Engineering Plastics, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100190, China University of Chinese Academy of Sciences, Beijing, 100049, P. R. China E-mail: [email protected]; [email protected]

ACS Paragon Plus Environment


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TOC image

Abstract Controlling of heterogeneous ice nucleation (HIN) on foreign surfaces is of great importance for anti-ice nucleation material design. In this work, we studied the HIN behaviors on various ion-modified poly(butylene succinate) (PBS) surfaces via chain-extension reaction. Inspired by antifreeze proteins (AFPs), the PBS-based polyampholytes, containing both negative and positive charge groups on a single chain, show excellent performance of ice nucleation inhibition and freezing delay. Unlike the extremely high price and low availability of AFPs, these PBS-based polyampholytes can be commercially synthesized under mild reaction conditions. Through the water freezing tests on a wide range of substrates at different temperatures, these PBS-based polyampholytes have application value of tuning ice nucleation via a simple spin-coating method. Keywords: heterogeneous ice nucleation, polyampholyte, poly(butylene succinate), bioinspired coatings, interface

1


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1. Introduction The undesired formation of ice always causes serious problems such as building damages, energy losses and safety risks of human beings.1-4 Current deicing strategies are mainly based on conventional thermal, electrical and mechanical approach to remove ice, which are costly, inefficient and environmental harmful.5, 6 To solve these problems, many passive anti-ice nucleation surfaces have been developed to delay heterogeneous ice nucleation (HIN), because nucleation is the first and rate-limiting step of the transition from water to ice.7-12 It has been reported that HIN can be controlled via changing the features of surface, such as the surface wettability, roughness, lattice parameter and local electric field.2, 8, 10, 13-21 Although a number of excellent experimental and theoretical works have been successfully carried out in pinning down the critical parameters for tuning HIN, only a few up-scalable coating materials are available for delaying ice nucleation. 13, 20-25 Nature has developed its own approaches to control ice formation, i.e., antifreeze proteins (AFPs) can protect organisms from freezing damage by controlling ice formation effectively.26, 27 Some recent attempts have been undertaken to introduce AFPs onto solid substrates to control HIN.28-30 Francis et al. attached AFPs to polymer chains in order to form polymer-protein conjugate coatings, which were able to delay ice freezing time as well as inhibit ice nucleation.28 Jin et al. also coated

Chaetoceros neogracile (Cn-AFP) on a metal material of aluminum. Compared to bare aluminum and other conventional hydrophilic aluminum coatings, the aluminum surfaces with surface-bound AFPs inhibited ice formation more efficiently.29 More recently, Liu et al. discovered the Janus effect of AFPs on ice nucleation via selectively binding AFPs to solid substrates. Most interestingly, they found that the water molecules atop the non-ice-binding face of AFPs exhibit disordered structure due to the existence of bulky hydrophobic groups and charged groups. Therefore, ice nucleation is energetically inhibited on top of the non-ice-binding face of AFPs.30 This has inspired the synthesis of AFP mimics with charged groups for HIN inhibition because of the extremely high price and low availability of AFPs as well as the 2



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labor-intensive surface modification method employed. 30-36 The polyampholytes, containing both negative and positive charge groups on a single chain, have been identified to good AFP analogues and show high 31, 37, 38

cryopreservation efficiency in the supercooled solutions.

Matsumura et al.

found that the combined effect of amino and carboxyl groups endowed polyampholytes with AFP activities, which contributed to successful cryopreservation by membrane protection.38 They also suggested that polyampholytes could be used as new materials for cryoprotective agents in various preserving functions. Mitchell et al. also synthesized an AFP inspired polyampholyte, and found that the polyampholyte with the ratio of cationic to anionic groups (1:1) exhibited maximum ice recrystallization inhibiting efficiency.31,

37

In this work, we prepared a series of

polyampholytes under mind synthetic condition, which exhibited excellent performance of ice nucleation inhibition and freezing delay. In order to improve the coating ability, thermal stability and processing properties of polyampholytes, the poly(butylene succinate) (PBS) prepolymer segments were incorporated into the polymer chains according to a chain-extension strategy.39,

40

Based on simple

surface-casting method, these polyampholytes will become promising candidates as anti-ice nucleation materials into environmentally friendly applications. 2. Experimental Section 2.1 Materials and film preparation Succinic acid and 1,4-butanediol were purchased from Beijing Chemical Reagents Corp. The catalyst of Titanium (IV) butoxide was distilled before use. Hexamethylene diisocyanate

(HDI)

were

purchased

from

Sigma-Aldrich.

2,2-Bis(hydroxymethyl)butyric acid (RC) and N-Methyldiethanolamine (RN) were purchased from Aladdin. The PBS-based derivative thin films were-spin coated with a chloroform solution of 10 mg/mL onto silicon substrates at 3500 rpm for 60 s. Silicon wafers were sequentially cleaned by sonication in ethanol, acetone, and ultrapure water before use. All ﬁlms were dried at vacuum oven at 30 oC for 12 hours to remove the residual solvent. The thicknesses of all different PBS-based derivative thin films were about 140-150 nm, which were measured by Ellipsometry (Woolam Co., Inc.). 3


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2.2 Chain-extension reaction Dihydroxyl-teminated PBS oligomer (PBS-diol) was prepared by esterification and polycondensation of succinic acid and 1,4-butanediol according to procedures proposed by Zheng et al.39,

40

The esterification of 1,4-butanediol (780.32 g) and

succinic acid (619.68 g) was carried out at 180 oC with catalyst of Ti(OBt)4 (0.28 mL) under nitrogen atmosphere. Then the polycondensation was carried out at 230 oC, and the pressure of the reaction device was gradually reduced to 5–15 Pa. The polymerization time lasted for 5 h to obtain the PBS-diol. PBS-diols were purified by repeated re-precipitation from their chloroform solutions by methanol, and dried for 24 h at 80 oC. The PBS-based derivatives were synthesized in bulk using HDI as a chain extender at 130 oC under nitrogen atmosphere for 0.5 h. For all the samples, molar ratio of –NCO to –OH was fixed at 1/1. The molar ratio of RC/PBS-diols for PBS-C and RN/PBS-diols for PBS-N were both set to be 1/1. The molar ratios of RC/RN/PBS-diols were set to be 0.5/0.5/1, 1/1/1, 2/2/1 for PBS-CN9, PBS-CN15 and PBS-CN28, respectively, as shown in Scheme 1 and Table 1. When the molar ratio of RC (or RN)/PBS-diols was more than 2/1, the coating was unstable during the multiple cycle freezing test. 2.3 Synthesis of other anti-ice nucleation coatings based on different surface modification strategies 2.3.1 Self-assemble Monomers (SAMs). Mercaptododecanoic acid (MDA), mercaptoundecanesulfonate

(MUS), trimethylammoniumundecanethiol (TAUDT),

mercapto oligo(ethylene glycol (MOEG) and mercaptoundecanol (MDC) were all purchased from ProChimia and used as received without further purification. Before preparing the SAMs on the gold surfaces, the silicon wafers evaporation deposited with gold were cleaned by plasma for 300s before use. Then the prepared gold wafers were immersed into the solution of the different functionalized thiols (MDA, MUS, TAUDT, MOEG and MDC,1mg/mL) without stirring for 10h and rinsed with ethanol and water. 2.3.2 Polymer Brushes (PBs). [2-(Methacryloyloxy)ethyl] trimethylammonium 4



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chloride (METAC, Sigma Aldrich), 3-Sulfopropyl methacrylate potassium (SPMA, Sigma

Aldrich),

[2-(methacryloyloxy)ethyl]-dimethyl(3-sulfopropyl)ammonium

hydroxide (SBMA, Sigma Aldrich) , 2-(2-Methoxyethoxy)ethyl methacrylate (OEGMA, Sigma Aldrich), Copper bromide (CuBr, 99.999%, Sigma Aldrich), 2,2’-bipyridine

(bpy,

99%,

Aladdin),

ethyl

2-bromoisobutyrate

(2-EBiB,

Sigma-Aldrich) were used as received. The bromo-substituted thiol initiator was synthesized by Suzhou Institute of Nano-Tech. The polymer brushes were prepared by a typical surface initiated atom transfer radical polymerization (SI-ATRP) method. Gold wafers were immersed into the solution of the thiol initiator (1mg/mL) without stirring for 8h and rinsed with ethanol and water. The polymer brushes of PMETA and PSPMA were synthesized with similar procedures as our previous work.9 The Cl− in PMETA brushes and K + in PSPMA brushes were exchanged with SO24− and Ca 2+ , respectively. The polymer brushes of PSBMA and POEGMA were synthesized according to the literature.41 2.3.3 Polyelectrolyte Multilayers (PEMs). Poly(ethylene imine) (PEI), Poly(acrylic acid) (PAA), Poly(diallyldimethylammonium chloride) (PDAD), poly(sodium 4-styrenesulfonate) (PSS) and poly(allylamine hydrochloride) (PAH) were all purchased from Sigma Aldrich without further purification. PEMs were performed according to the LBL deposition method. A layer of PEI was firstly deposited onto the substrate before the subsequent LBL deposition. Then the as-prepared substrates were dipped in polyanion solutions (PAA and PSS, 1.0g/L) for 30 min and polycation solutions (PDAD or PAH, 1.0g/L) alternatively. The substrates were rinsed by NaCl solutions (0.5M) between each deposition process. Dipping and rinsing steps were alternated and repeated until the desired layers were obtained. 2.4 Characterization 2.4.1 Proton Nuclear Magnetic Resonance Spectroscopy (1H NMR). The chemical structures of the PBS-diol were characterized by a Bruker Model DMX-400 NMR spectrometer using CDCl3 as the solvent and tetramethylsilane as the internal standard. The peaks at 1.67 (δH), 2.65 (δH), and 4.10 (δH) ppm are corresponded to three 5


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different types of methylene protons in the repeating monomers of PBS-diol as shown in Figure S1. 2.4.2 Gel Permeation Chromatography (GPC). The number-average molecular weight (Mn) and polydispersity index (PDI) of different PBS-based derivatives were measured by a Waters Model 2695 GPC gel permeation chromatography using polystyrene as a standard. Chloroform was used as the fluent at a flowing rate of 1.0 mL/ min. 2.4.3 Differential Scanning Calorimetry (DSC). The melting temperatures, glass transition temperatures and melting enthalpy change ( ∆H m ) of different PBS-based derivatives were performed on a calorimeter (TA Q2000) under nitrogen atmosphere at a cooling/heating rate of 10 oC/min. 2.4.4 Elemental Analysis. The atomic concentrations (C, N and H) of different PBS-based derivatives were measured with a Vario EL elemental analyzer (Elementar, Germany). The molar ratios of RC and RN were estimated by the atomic concentrations (C, N and H). 2.4.5 Atomic Force Microscope (AFM). The surface morphology and roughness were characterized by atomic force microscope (AFM). The surface morphology and roughness were conducted on AFM (Bruker Multimode 8) via ‘peak force tapping mode’. 2.4.6 Contact Angle (CA) Measurements. The static contact angle measurements were measured by a drop size analyzer (DSA-100, KRÜSS, Germnay). The images were captured by an optical microscope precisely 60 seconds after the contact of a droplet with the different PBS-based derivatives. 2.5 Water freezing measurement The HIN temperature (TH) and freezing delay time (tD) on PBS-based derivative surfaces were detected by the home-made experimental apparatus with a microscope coupled with a high speed camera (Phantom v7.3) and a closed cell placed atop a cryostage (Linkam THMS 600) (see in Figure S2).9 The sample cell was composed of a rubber O-ring sandwiched between two cover glasses. Because the volume of the 6



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closed cell is small enough (with a volume of 0.283 cm3), the water droplet thermodynamically equilibrates with the water vapor. Before the HIN tests, the identical sized water droplet (with a fixed volume of 1.0 µL) was placed atop the PBS-based derivative surfaces, as such the effect of heterogeneous ice nucleation (HIN) on different PBS-based derivative surfaces could be compared. The whole sample-preparation process was carried out in a bio-safety cabinet to minimize possible contaminants. The as-prepared samples were cooled down from room temperature at different cooling rates on a cryostage with a microscope coupled with a high speed camera. The time resolution is 1 ms, i.e., 1000 frames per second, and the temperature resolution is 0.1 oC, respectively. The temperature at the onset of ice nucleation was identified through a video recorded by the high speed, which is determined as TH. The tD is defined as the time interval between the time when the PBS-based derivative surface reaches the preset temperature and that when the ice nucleation occurs. The tD is measured at target temperature (-25.0 oC) when temperature is lowered from the room temperature at a cooling rate of 5.0 oC/min. All the results of the TH and tD are the mean of more than 200 independent freezing events for each PBS-based derivative surface. The error bars are the standard errors of the mean, and the distribution of TH and tD are consolidated by the student’s t-Test. 3. Results and discussion Synthsis and characterization of PBS-based polyampholytes PBS-diol was prepared by esterification and polycondensation of succinic acid with 1,4-butanediol based on catalyst Titanium(IV) butoxide (see Scheme 1a) as similar procedures proposed by Zheng et al.39, 40 The molecular weight of PBS-diol was tuned to ~5000 (detected by 1H NMR) by controlling the polycondensation time. The chemical structure of PBS-diol was characterized by 1H NMR spectra (in Figure S1). The series of PBS-based derivative were designed and synthesized via melt chain-extension reaction in the presence of HDI as a chain extender at 130 °C. By regulating the feed molar ratios of PBS-diol, carboxyl-based group of RC and amino-based group of RN, the chain-extented PBS-diol (PBS), the carboxylated PBS (PBS-C), the aminated PBS (PBS-N) and polyampholytes with random blocky 7


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carboxyl and amino groups (PBS-CN) were prepared (in Scheme 1b). Polyampholytes with different contents of RC (or RN) is designated as PBS-CNx, where x is the molar ratio between 10×RC (or 10×RN) and PBS-diol determined by elemental analysis (in Table 1 and Table S1). In order to obtain a net neutral charged state of polyampholytes, the content ratio of RC and RN in PBS-CN were controlled as 1:1. Because the charge balance of polyampholytes is investigated to be crucial to the antifreeze activity.37 The number-average molecular weight (Mn) and molecular weight distribution (PDI) of PBS-based derivatives were determined by GPC (in Table 1). The melting temperature (Tm) related to the crystallization of the PBS segment (Tm around 110 oC) were assessed by DSC (in Table 1 and Figure S3). The melting enthalpy values ( ∆H m ) of PBS-CNx samples are almost the same, which are different from those of PBS, PBS-C and PBS-N. It is suggested that the crystallinity of PBS-based derivatives are influenced significantly by the charge characteristic of polymer chain. Meantime, the glass transition temperatures (Tg) of PBS-based derivatives change when different charged groups are introduced into the PBS chains. The PBS-based derivative surfaces for ice nucleation tests were prepared via simple spin-coated method. Figure S4 shows the surface morphology and average surface roughness (Ra) of PBS-based derivative surfaces detected by AFM. All the values of Ra are less than 7 nm, exhibiting relative smooth surfaces. We further studied the hydrophilicity of the PBS-based derivative surface as shown in Figure S5, and found that the static contact angle decreases as the content of RC (or RN) increases.

8



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a O OH

HO

+

_

HO

O

H2O

HO

OH

O

O

160 oC £¬1 atm

O

nOH

O

(PBS-diol)

O HDI

O

[ PBS

b

N( )

O ]

N

6

(PBS)

n

O O

HDI + RC

PBS ]

[

m

N( )

O

6

O [

N

RC ]

(PBS-C) n

O

PBS-diol +

O

HDI + RN [

PBS ]

m

N( )

O

6

O [

N

(PBS-N)

RN ] n

O O

HDI + RC + RN

[

RC ] O

N( )

n

6

O O [

N

PBS ] m O

O

(

HDI :

O C N

N C O

N( )

6

N

O [

RN ] n

(PBS-CN)

O

RC :

HO

OH O

RN :

HO

N

OH

)

OH

Scheme 1. Synthsis of (a) PBS-diol and (b) PBS-based derivatives with variable functional groups.

Table 1. Characterization data of PBS-based derivatives.

a

Sample

PBS-diol/RC/RNa

Mnb

PDIb

Tm (oC)c

∆ H m (J/g)c

Tg (oC)d

PBS

1/0/0

90000

1.3

110.2

54.3

-34.5

PBS-C

1 / 1.8 / 0

50000

1.8

110.6

72.5

-31.5

PBS-N

1 / 0 / 1.6

53000

1.7

107.4

46.5

-33.2

PBS-CN9

1 / 0.9 / 0.9

50000

1.8

110.4

63.9

-31.5

PBS-CN15

1 / 1.5 / 1.5

65000

1.5

109.7

63.4

-31.1

PBS-CN28

1 / 2.8 / 2.8

48000

1.6

110.4

63.2

-36.9

Determined by elemental analysis. bDetermined by GPC. c,dDetermined by DSC.

Ice nucleation Ice nucleation in the water drop started at the solid/water interface, followed by the upward ice growth as shown in Figure S6. HIN of water droplets can be signified by a 9


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sudden change in opacity before and after freezing. In-situ optical microscopic observation of water droplets shows that different PBS-based derivative surfaces have different effects on the HIN as shown in Figure S7. All the results on the TH were based on more than 200 independent freezing events for each PBS-based derivative surface. The distributions of TH on all PBS-based derivative surfaces approximately follow the normal distribution as shown in Figure 1a. The error bars are the standard errors of the mean, which is the standard deviation of the sample-mean's estimate of a population mean. As shown in Figure 1b, it can be found that the TH on the PBS-C, PBS-N, PBS, PBS-CN9, PBS-CN15 and PBS-CN28 surfaces are -24.5 ± 0.6 oC, -24.8 ± 0.5 oC, -26.7 ± 0.7 oC, -27.3 ± 0.4 oC, -29.7 ± 0.4 oC and -29.8 ± 0.5 oC, respectively, exhibiting a TH window up to 5.2 oC. The TH of water droplet on the polyampholyte surfaces is lower than that on other PBS-based derivative surfaces. Meanwhile, the TH decreases with the contents of RC or RN. The effect of the cooling rate (from 1.0 oC/min to 10.0 oC/min) on the HIN was also studied as shown in Figure 1c, showing the same trend of TH, i.e., TH,PBS-C > TH,PBS > TH,PBS-CN28. a

b

c

-32

-30 0.25

PBS-C PBS PBS-CN28

0.05

-28

-26

TH (oC)

TH (oC)

0.15 0.10

Probab ility (%)

-30 0.20

-28

-26

-3 0

H ( oC)

-24

2

4

6

8

10

Cooling Rate (o C)

-3 2

-2 6

-24

T

-2 8

-2 2

0.00 -2 4

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 1. (a) The distribution of heterogeneous ice nucleation temperature (TH) on different PBS-based derivative surfaces (PBS-C, PBS and PBS-CN28). (b) The TH of different PBS-based derivative surfaces. (c) The influence of cooling rate (from 1.0 o

C/min to 10.0 oC/min) on the TH of different PBS-based derivative surfaces (PBS-C,

PBS and PBS-CN28). The substrates are silicon wafers.

In order to consolidate the ability of different PBS-based derivative surfaces in tuning the HIN, we further studied the corresponding delay time (tD) at -25.0 oC. As shown in Figure 2a, the HIN induction time was significantly different on PBS-C and 10



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PBS-CN28 surfaces, e.g., water frozen immediately (within 3 s) on PBS-C surface (upper row), in contrast, the water drop did not freeze until 9560s later on PBS-CN28 surface (bottom row). The tD of water droplets on different PBS-based derivative surfaces shows the order of tD,PBS-CN28 > tD,PBS-CN15 > tD,PBS-CN9 > tD,PBS > tD,PBS-N > tD,PBS-C as shown in Figure 2b. It is noted that the increase of the tD is consistent with the decrease of the TH (see in Figure 1b and Figure 2b). Compared with other PBS-based derivative surfaces, the polyampholyte surfaces exhibit high performance of ice nucleation inhibition and freezing delay.

Figure 2. (a) Optical microscopy images of HIN at -25.0 oC on the PBS-based 11


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derivative surfaces of PBS-C and PBS-CN28 (The scale bar is 200 µm). (b) The freezing delay time (tD) of water droplets on different PBS-based derivative surfaces. The substrates are silicon wafers.

As stated above, the TH on the PBS-CN28 surface can be well-controlled at relative low temperature of -29.8 ± 0.5 oC, and the water droplet is able to keep up unfrozen for ~9500s at -25.0 oC, exhibiting good performance of inhibiting HIN. A comparison of TH on PBS-CN28 surface with reported surfaces capable of tuning HIN based on different surface modifying strategies (SAMs, PBs and PEMs) is shown in Figure 3. Some works have investigated that the HIN of water or aqueous NaCl droplets is strongly determined by the structure of coated monolayers.42-44 We prepared SAMs with typical functional headgroups like carboxylic acid (MDA), sulfonic acid (MUS), quaternary ammonium (TAUDT), ethylene glycol (MOEG) and alcoholic hydroxyl (MDC) as shown in Figure 3a. The lowest TH of -25.6 ± 0.7 oC is observed on the surface of MOEG, which is higher than that on the PBS-CN28 surface (Figure 3a and d). Recently, we studied the ion-specific effect on HIN, and found that the TH on polyelectrolyte brushes can be modulated by different counterions.9 By varying various counterions, the PMETA brush with SO24− has lowest TH of -23.9 ± 0.7 oC and PSPMA brush with Ca 2+ has lowest TH of -24.5 ± 0.5 oC, respectively. The TH on polymer brushes of PSBMA and POEGMA are -21.5 ± 0.7 oC and -23.1 ± 0.6 oC, respectively (Figure 3b and d). Due to the labor-intensive surface anchoring modification of SAMs and PBs, we further studied HIN on PEMs based on the simple layer-by-layer (LBL) deposition process. For PEMs of PAA/PDAD and PSS/PAH with different outermost layers, the values of TH are all above -25.0 oC as shown in Figure 3c and d. At last, we compared the value of TH on PBS-CN28 surface with that on various AFP tethered surfaces (TH on various AFP tethered surfaces were measured in our previous study) 30, and found that the TH of PBS-CN28 was higher than the TH of beetle Microdera punctipennis dzungarica (MpdAFP) and Marinomonas primoryensis (MpAFP), but lower than that of a moderate active fish AFP (type III 12



AFP). Obviously, the PBS-CN28 surface has higher ice nucleation inhibition efficiency than the coatings of SAMs, PBs and PEMs, exhibiting a close performance of inhibiting ice nucleation to the AFPs. More importantly, the polyampholyte of PBS-CN28 can be coated on almost all the substrates via a simple spin-coating method, forming stable HIN inhibition coatings.

a

TAUDT HS

b

MUS

+ N

( )9

Cl-

HS

( )9

( )O 11

( O

)n O

+

SO-3 Na+

MDC

HS ( )8

HS

O

( )O 11

MOEG HS

PSBMA

( O

( )9 OH

HS

PSPMA

PMETA

HS

MDA HHHH OOOO OOOO CCCC

)n O

O

N SO42-

HS

( )O 11

PEGMA

( O

)2OH

( )9 ( O

)n O

O

HS

( )O 11

( O

)n

+ N

2+ SO3 Ca

O

O O

O SO3

c

PSS

PAH

PDAD n

PAA

Cln n

N H 3C

CH 3

NH2

n

O

OH

SO-3 Na+

d -33 -30 o

TH ( C)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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Self-assembly Monomers

Polymer Brushes

Polyelectrolyte Multilayers

-27 -24 -21 -18

Figure 3. The surface structures of (a) self-assembly monolayers (SAMs), (b) polymer brushes (PBs) and (c) polyelectrolyte multilayers (PEMs). (d) Comparison of TH of PBS-CN28 with different antifreeze proteins (AFPs) and other materials based on different surface modifying strategies.

13


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In fact, an effective anti-ice nucleation coating should be able to adapt to different substrates. Therefore, we studied the HIN inhibition efficiency of PBS-CN28 coated on different substrates. Figure 4a shows the TH on various substrates such as glass, ceramic, silicon, plastic, rubber and metal surfaces before and after spin-coated with PBS-CN28. It is obvious that the TH reduced substantially when PBS-CN28 coated on different substrates. To further consolidate the ice nucleation inhibition effect of PBS-CN28, we further studied the corresponding tD at -25.0 oC as shown in Figure 4b. The water drop atop almost all the substrates, except the silicon substrate, froze immediately before the temperature reached -25.0 oC as the temperature was lowered from the room temperature at a cooling rate of 5.0 oC/min. The value of tD on the silicon substrate is about 1600 s. In strong contrast, all the values of tD on the PBS-CN28 coated surfaces are more than 8000s. It demonstrates clearly that the coating of PBS-CN28 has potential application value of inhibiting ice nucleation on a wide range of substrates. a

Uncoated Coated

Ceramic Polyethylene

-20

Polyimide

o

Glass

Copper Aluminum

Polydimethyl siloxane

-25 Silicon

15000 Freezing Delay Time (sec)

-15

TH ( C)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Uncoated Coated

b

12000 Ceramic

Polyethylene

Polydimethyl siloxane

Aluminum

9000

6000 Glass

Silicon

Polyimide

Copper

3000

-30 0 1

2

3 4 5 6 Different Substrates

7

8

1

2

3

4

5

6

7

8

Different Substrates

Figure 4. The (a) TH and (b) tD on a wide range of substrates before and after spin-coated with PBS-CN28.

In real world, when the temperature is lower than the dew point, plenty of freezing events of water microdroplets will form on the chilled surface, causing great difficulty in surface HIN inhibition strategy. Therefore, the test of freezing delay time on surfaces in real environment is critical to many anti-ice nucleation applications. We studied the freezing delay times on various PBS-C and PBS-CN28 coated substrates at different temperatures when the humidity was fixed at 20% ± 2%. As shown in 14



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Figure 5a, all the condensed water droplets froze in a short period (within 300s) on the PBS-C surface at -16 oC. In strong contrast, no ice crystals formed on the PBS-CN28 surface until water condensed continuously for almost 2400 s as shown in Figure 5b. We further measured the freezing delay times as the function of temperatures (from -12 to -20 oC) as shown in Figure 5c. The freezing delay time on PBS-CN28 surfaces increased from 400s ± 150s to 7800s ± 2600s with the increasing of temperature from -20 to -12 oC. Meanwhile, all the freezing delay times on PBS-CN28 surfaces were longer than that on PBS-C surfaces at any temperature. The freezing delay times on PBS-C and PBS-CN28 coated glass, metal and polymer surfaces were also investigated as shown in Figure 5d. The freezing delay times on PBS-CN28 coated surfaces were observed to be almost ten times longer than that on the PBS-C coated surfaces. It is noted that the coating of PBS-CN28 has potential application value of tuning ice nucleation under different conditions. In future, more chemical modifications and coating processing methods will be utilized to improve the long-term stability and surface-bound property of PBS-based polyampholytes.

Figure 5. Freezing of condensed water on (a) PBS-C and (b) PSS-CN28 surfaces at 15


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-16 oC for 1) 30 s, 2) 300 s, 3) 2400 s and 4) 3100 s at humidity of 20% ± 2%. The scale bars are 50 µm and 2 mm in the main and insert figures, respectively. (c) The freezing delay times on the PBS-C and PSS-CN28 surfaces at different temperatures when the humidity is 20% ± 2%. (d) The freezing delay times on the PBS-C and PBS-CN28 coatings on different substrates at -16 oC when the humidity is 20% ± 2%. Conclusion Inspired by the AFPs, we have synthesized various PBS-based derivatives, especially the PBS-based polyampholytes with the ratio of amino to carboxyl groups (1:1). We found that the PBS-based polyampholyte coatings have potential application value of inhibiting ice nucleation on a wide range of substrates. Compared with other labor-intensive AFP-attached surface modifications, the PBS-based polyampholytes can be coated on almost all the substrates via a simple spin-coating method. It is estimated that these PBS-based polyampholytes will become promising candidates as anti-ice nucleation materials.

Supporting Information 1H NMR spectrum of PBS-diol; the experimental apparatus; the melting behaviors, surface morphology, roughness, contact angle and elemental analysis of PBS-based derivative surfaces; optical microscopic observation of freezing of a water droplet on PBS-based derivative surfaces.

Acknowledgements We gratefully acknowledge the financial support from the 973 Program (2012CB933801) and the National Natural Science Foundation of China (51436004, 21421061, 21503240, 21574137). References [1] Lv, J.; Song, Y.; Jiang, L.; Wang, J. Bio-Inspired Strategies for Anti-Icing. ACS Nano 2014, 8 (4), 3152-3169. [2] Kreder, M. J.; Alvarenga, J.; Kim, P.; Aizenberg, J. Design of Anti-Icing Surfaces: Smooth, Textured or Slippery? Nat. Rev. Mater. 2016, 1, 15003. [3] Bizjak, K. F.; Dawson, A.; Hoff, I.; Makkonen, L.; Ylhäisi, J. S.; Carrera, A. The Impact of 16



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Inhibition of Heterogeneous Ice Nucleation by Bioinspired Coatings of

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